EU chief negotiator Brexit voiced his concerns at a meeting of EU legislators, a person familiar with the situation told Reuters.
Michel Barnier reiterated that Prime Minister Theresa May must make compromises to reach an agreement between the EU and the UK.
On Wednesday, he tweeted that he "works for an orderly Brexit and a new partnership that respects the sovereignty of Britain, as well as the founding principles of the EU, such as the integrity of the single market.
A diplomat involved in Brexit talks said that confidence that a deal is imminent is beginning to decline.
The extension of the negotiation period under Article 50 may prove inadequate, but could be substantial
He said, "I'm less optimistic now, I'm not so sure anymore."
This happened after a high-ranking official for the President of the European Commission, Jean-Claude Junker, had urged the EU ambassadors from the remaining 27 member states to deal with an abrupt British departure.
According to Reuters, diplomats and officials said the final round of talks was a sign of determination to deal with a "hard Brexit" if Britain refused to bow to EU conditions.
However, there are differing views as to whether this signaled greater urgency or fears of no-deal brexits.
An EU diplomat said, "There is a desire not to rock the boat with too much 'no deal' attitude.
"It's just a calendar problem – if we want to be sure that we're prepared, we have to move on."
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Brexit: Michel Barnier has doubts as to whether a deal can be reached by its deadline in mid-November
8.31 am Update: Tory Brexiteer asks Mai to resign
Nadine Dorries has called Theresa May to resign and accused the Prime Minister of abandoning the people because "she has tied herself to this Checkers deal."
The Brexiter and MP for Mid-Bedfordshire, who appeared on the ITV's Peston program, was asked if she believed Mrs. May should go, to which she responded.
Mrs Dorries added: "I think if we do not, I'll say it in mourning, because I was glad when Theresa May was Prime Minister and I told people many, many months ago, trust her, she'll deliver & # 39 ;.
"Unfortunately, she let me down and she failed other people because she does not deliver, she does not deliver because she got tied up with this checkers deal."
The MEP also repeated the comments of the former Minister and Mark Francois colleagues that the Tory Eurosceptics would refuse to support the May Checkers plan.
Ms. Dorries added, "The prime minister must climb down and she must support a Canada plus FTA."
Update at 19:02: EU Ambassadors meet for a "closed session" to discuss the implications of the Brexit No deal – Report
The EU ambassadors will hold a rare "closed session" on Wednesday evening to discuss the prospects of the British Parliament rejecting the final divorce settlement.
Discussion topics include possible sub-deals to keep planes, medicines and ports moving.
The talks are reportedly focused on using the legal basis of the Article 50 exit talks to absorb the effects of a no-deal if it turns out that the negotiations are stalling and time is running out before Britain closes the bloc on 29 May March leaves, 2019.
A limited agenda, seen by the Times, reads: "Preparatory work needs to be stepped up in the coming months, both at national and EU level, as there is uncertainty over the outcome of the negotiations and the ratification of a possible agreement."
18.12 Update: Barnier backtracks mid-November deadline for the final Brexit deal
Michel Barnier has reportedly been in doubt as to whether his mid-November goal of agreeing a framework contract and a definitive package with the UK will be respected, raising further doubts as to whether a Brexit agreement will be concluded.
Brexit's EU chief commissioner granted approval to EU lawmakers on Tuesday, Reuters told reporters.
The EU politicians who rejected Theresa May's Checkers' plan last week at a summit in Salzburg insisted on making compromises.
A diplomat involved in Brexit talks said his confidence that a deal was imminent had receded.
"I'm less optimistic now, I'm not so sure anymore."
This happened after a senior official of the European Commission President, Jean-Claude Junker, had informed the ambassadors of the remaining 27 Member States about plans to overthrow the United Kingdom without agreement.
17:47 Update: Irish Finance Minister warns of "considerable shock" for the economy with no-deal Brexit
The Irish Finance Minister warned against a no-deal Brexit, which would be a "major shock" to the booming economy in the country.
Paschal Donohoe said that if Great Britain fell out of the bloc without an agreement with Brussels, the Republic's productivity would grow by only 2-3 percent instead of 3-4 percent.
He said Ireland would also be exposed to "exceptional fluctuations" in the value of sterling, which would affect trade.
Mr Donohoe added that a disorderly Brexit would hit the Irish financial sector in areas such as cash flow and insurance contracts.
The United Kingdom is Ireland's main trading partner – around one third of the country's exports go to the Irish Sea.
The Finance Minister, who provided evidence to the Special Committee on the Budgetary Control of Ireland, warned: "This would be a very significant shock to our economy.
"It's likely that our economy will continue to grow, but at a much lower rate."
He predicted a "major structural change" in Ireland's economic relations with Britain after the divorce, adding, "There will be many new commitments for Irish, European and British companies."
Mr Donohoe also reiterated that more customs and agricultural officials are needed.
Brexit: Philip Hammond has pushed forward the turn of the autumn to avoid a collision with an important Brussels Summi
16:48 update: The autumn budget was postponed to the 29th October, to collide with the crucial Brexit summit
Philip Hammond has postponed his fall budget to October 29 to avoid conflict with the Brexit talks, the Financial Times said.
The budget would come just a week after a crucial Brexit summit in Brussels on 18 October, where a definitive Brexit deal could be undermined. It would also be three weeks earlier than last year
The Chancellor is expected to use economic policy to calm markets, while the UK is preparing to leave the EU.
Mr. Hammond said on Twitter: "I will outline how our balanced approach will lead to debt reduction while supporting our vital public services and building a stronger, more prosperous economy."
4.11pm update: Business leaders tell May about "daunting" Brexit
Business leaders have told Theresa May of her fears of Brexit and asked for further assurances from the Prime Minister.
Ms. May had gone to the stage at a gathering of corporate executives in New York to sell the best tax-advantaged, high-qualifying place after Brexit Britain.
But during a question-and-answer session following their speech, Steve Schwarzman, CEO of investment firm Blackstone, warned that Britain's exit from the EU was "daunting."
He said, "In terms of downside management, we just bought something in the UK last week, so I believe we are believers.
"But on the other hand, things could end well with a poor Brexit and also a change of government.
"The thing we really care about is how bad things can get?"
"We believe in the good cause, but in terms of risk-taking it is a bit intimidating for us outsiders."
IBM boss Ginni Rometty asked the Prime Minister about the risks of a bad Brexit.
She said, "We all work in the area of corporate risk management and we talk about Brexit.
"What would you do in our shoes to plan now, what would you do now to offset that risk?"
Brexit: Jeremy Corbyn warned that a collapse of the EU would be a "national disaster"
15:46 Update: Pound falls slightly, but analysts remain optimistic
The pound fell on Wednesday as investors remained cautious in the negotiations between Brint and the EU over a Brexit deal.
The pound sterling slipped marginally 0.1% to $ 1.3171, but will be above the $ 1.3041 low that collapsed last Friday.
The currency gained 0.2 percent to trade at 89.14 pence per euro, which initially fell against the single currency that weakened trade in New York.
Michael Hewson, senior market analyst at CMC Markets, said: "The pound has continued its recent recovery following the sell-out late last week.
"The fear that we might see another election seems to have vanished for the time being after Prime Minister Mai questioned the idea on the way to the United Nations in New York."
15:25 update: Flights between Ireland and Great Britain could be cleared, warns the aviation chief
Flights between Ireland and the UK could be put on hold in the event of a no-deal Brexit, warned the head of the Irish Aviation Authority.
On Wednesday, Michael McGrail, chair of the Irish Aviation Authority (IAA), reported in his report to the country's Transport, Tourism and Sports Committee on the challenges facing the industry and warned that the impact would begin at midnight on 29 March Date The United Kingdom is leaving the EU.
He said: "Given the obvious deadlock between the UK and the EU, a satisfactory withdrawal agreement, transitional period and then future relationship is in question," he said.
"Apart from the disruption to aviation and the traveling citizens, a serious Brexit would have a significant negative impact on our economy as a whole.
"The Department of Transportation is undertaking a scenario planning to ensure minimal negative impact, and the ILO is working closely with the department and other agencies in this regard."
Expressing the practical implications for the public, and whether a Brexit without a deal would lead to a sudden end to the flights, McGrail added: "If there is a hard Brexit, the UK will become a third country and with it the air traffic management and aviation safety regulations, currently not only in the UK, but in the rest of Europe, would be eliminated.
"There are obviously immediate practical problems that I suspect at midnight on March 29th.
"Knowing that the Department is working on workable solutions, they have a number of scenarios to study, and we work closely with them to see how these scenarios actually work.
"The IAA and the Irish government can control that, it's very much the EU."
Theresa May talked to business people in New York
14:47 update: Corbyn & # 39; unable to govern & # 39 ;, says Tory Chairman
Conservative leader Brandon Lewis has blasted the prospect of Jeremy Corbyn, who becomes prime minister, with the working families having the most influence.
He said, "Jeremy Corbyn has shown at every opportunity that he can not govern.
"Everything he offers is failed ideas that did not work in the past and that would make working families pay the price with higher taxes, more debt, and more waste – just like last time."
14:33 update: Corbyn has thrown away the Tories & # 39; the gauntlet
Eloise Todd, director of the Best for Britain program for a second referendum, praised the speech by Jeremy Corbyn and called for a "referendum with the option to stay".
She said: "Jeremy Corbyn has thrown the Tories the gauntlet by challenging them to pass the six tests of Keir Starmer, but it's clear that this government can not do that, the extreme Brexitians in the Tory party can not.
"No form of Brexit can deliver the six tests or what Labor wants – the current impasse in Parliament and in negotiations with the EU shows that. Only our current agreement with the EU can pass these tests.
"So the only way out of this mess is to stick to a referendum with the option to vote, and then the public can compare our current tailor-made deal to what brings that government together."
14:26 update: Laboratory will offer Scotland "economic chaos and incompetence" – SNP
The SNP's Westminster leader, Ian Blackford, has blasted the Labor Party's plans for Scotland, claiming that they "are not fit for the opposition, let alone the government.
He said, "Labor has proven that they can offer Scotland nothing, but economic chaos and incompetence – fails to offer the Tories a meaningful alternative.
"After a bitter conference dominated by disputes over Brexit, racism and sectarianism, Labor has shown that they are not even fit for opposition, let alone government."
Jeremy Corbyn hands over his Brexit vision of the Labor Party conference
2.10 am Update: & # 39; We will vote! & # 39; Labor MP warns of May's Brexit plan
Shadow Minister Dawn Butler warned that Theresa May would not be able to get a good Brexit deal and that Labout would "vote".
She said: "We want to clarify what is at stake here – we have already said that we must protect our standards and services, workers' rights and jobs.
"The six steps still stand and it is up to the Prime Minister to negotiate a good deal or we will reject him."
2.01 am Update: "Big boost in the conference" – shadow house secretary John Healy
John Healy welcomed the "big boost" of the Labor Conference and added that the party was "ready to negotiate on Brexit and lead Britain".
The shadow house secretary told the press association: "There is a big boom at the conference, it's part of the whole week when Labor is working out a plan on what we in the government will do to rebuild the country.
"Mr Corbyn has today made a big challenge for Theresa May to Brexit.
"We have consistently said over the course of a year the tests that a good deal has to meet, and if it recognizes that, makes a deal, and holds those tests, we will support them in Parliament.
"If she can not make a deal that meets those tests, we'll fight it if she can not make a deal coming through Parliament, then she has a choice – we need to change the team, not just the plan and we are ready to negotiate on Brexit and lead the UK. "
Asked which option is most likely, Mr Healey said, "No one knows that honest answer" before Labor is clear about the issues it will question.
Brexit: Michel Barnier will hold talks tomorrow after the Labor Party Conference
Paul Withers takes over live coverage of Simon Osborne.
2.03 clock update: May is aimed at executives in New York
Theresa May told executives at a business forum organized by former mayor of New York, Michael Bloomberg, that "a Britain after Brexit is going to be a pro-business Britain".
The PM said that companies investing in the UK receive the lowest corporate tax rate in the G20.
She said, "You will have access to service industries and a financial center in London that will give us the envy of the world, the best universities, strong institutions, a solid approach to public finances, and a consistent and reliable approach to high standards, but smart ones Regulation is. "
Ms May said her Checkers proposals "have a lot in common" with the EU, despite their rejection at an informal summit of trade union leaders last week in Salzburg.
She said, "There is no other plan that protects jobs and livelihoods, and also meets our commitments in Northern Ireland, while respecting the way people have voted in the biggest democratic exercise in our history.
"With the completion of negotiations in the coming weeks, the certainty of a deadline for implementation to adapt to the new regulations and ensuring smooth trade with the EU in the future, the economy can look forward to the post-Brexit world with confidence."
Brexit: Brandon Lewis beating Jeremy Corbyn and claiming he is "unable to govern"
1:36 pm Update: Tories react to Jeremy Corbyn's Brexit comments
The conservatives responded Jeremy Corbyn's conference talk on social media.
They tweeted: "Right now @ Jeremycorbyn claimed Labor would respect the outcome of the EU referendum …
"But yesterday he supported @Keir_Starmer, who said that no one leaves, stay & # 39 ;.
"It is clear that they would bring us all back to Brexit."
1.30 pm Update: Corbyn – "Brexit is about the future of our country and our vital interests"
Jeremy Corbyn told the Labor Conference that his party respects the British people's decision in the EU referendum, but warns that a collapse of the EU would be a "national disaster".
He told delegates in Liverpool, "Our priority is clear: we want to reach the best Brexit job and living standards deal to support our plans to improve the economy and invest in every community and region.
"This can bring people together and fulfill the concerns of those who have elected as well as those who have elected.
"We will vote against any reduction in rights, standards or safeguards and oppose deregulation.
"The Labor Party will vote against the Checkers plan or whatever it may be and vote against the EU not making a deal.
"And it is inconceivable that we would launch from Europe without a deal – that would be a national catastrophe."
12:14 pm Update: Barnier and Corbyn give lectures
EU chief commissioner for Brexit, Michel Barnier, has announced that he will meet Labor leader Jeremy Corbyn.
Barnier's office said the couple will hold talks tomorrow after the Liverpool Labor Party conference.
The meeting took place after Mr Corbyn and his shadow bank team distanced themselves from the speech of a second EU referendum.
11.45 am Update: Raab meets Gibraltar's Fabian Picardo
Brexit Secretary Dominic Raab had talks with Gibraltar's Prime Minister Fabian Picardo.
Mr Raab said: "I was very pleased to welcome Mr Picardo to a discussion on the common opportunities that will arise when the United Kingdom and Gibraltar leave the EU together.
"We had a productive conversation about the importance of GB-Gibraltar relations and the important work to deepen and strengthen it in the future.
"The UK fully participates in Gibraltar as we negotiate to leave the EU, and this meeting was just one of many ways we can ensure that its priorities are taken into account.
"I look forward to working together to ensure a successful future for the UK and Gibraltar outside the EU."
Dominic Raab welcomes Fabian Picardo
10:22 am update: Labor numbers reduce the chances of a second referendum
Senior Shadow Cabinet members distanced Labor from a second Brexit referendum on the day after the party delegates voted to keep the option on the table.
Rebecca Long-Bailey, the shadow executive, said the party would not launch a new referendum in its manifesto unless a general election had been called before March.
Ms. Long-Bailey told BBC Radio 5 Live that Sir Keir's application, which was negotiated after a late-night meeting, respected the 2016 referendum.
When asked if a new poll would be part of a list of campaign promises when Theresa May sent the country to the polls before Brexit Day in March, she said no.
She added that a second referendum was "hypothetical" and added, "What we said is that under very extreme circumstances, nothing should be ruled out, and that involves people voting."
She said it was not impossible for Labor to vote for a deal by the Prime Minister, but added that "we are a long way from anything that could bring the party back."
09:03 Update: Labor "accepts and respects" the Brexit decision
Shadow Justice Secretary Richard Burgon said the Labor policy remained: "We accept and respect the outcome of the referendum".
Asked on LBC radio about Sir Keir Starmmer, who left the door open for a second poll, he said, "Who knows where the story is going?"
He added, "The Labor Party does not demand a second referendum.
"Labor has our own vision of Brexit, respects and accepts the outcome of the referendum."
8.30 am update: Labor MP warns against "election risk" of ignoring the referendum result
Labor Brexiter Graham Stringer warned that there could be "real electoral danger" if the result of the EU referendum were not implemented.
The MP for Blackley and Broughton told BBC Radio 4's Today program: "I think the actual resolution, supported yesterday, was a classic Labor Party conference.
"I think there are real electoral dangers when we start resorting to this commitment, not just not by many voters and voters who have voted for Labor in the past and Leave, but also democracy among the voters just respecting the decision and We want to stick to it because all the big party leaders have committed to holding the referendum. "
When asked if he would support the Prime Minister when making a deal, he said, "It all depends on what the deal is.
"If she continues with the nonsense of Checkers, no, I would vote against.
"If it meets the manifesto obligations of the Labor Party and the expectations of the referendum, I am a Democrat, I would respect this referendum decision."
7.30 am Update: French minister says EU future more important than Brexit
French Finance Minister Bruno Le Maire said the EU has more pressing priorities than Britain's future relations with Brussels.
EU leaders have rejected Theresa May's post-Brexit proposals and firmly believe that the plan would undermine the single market.
Mr Le Maire said: "The British have made their choice, that's fine.
"Excuse me for saying so brutally, but there are more important things for us than the future of the UK, it is the future of the European Union.
"Any decision that gives European citizens the impression that they can leave the European Union and retain all the benefits would be suicidal."
7 pm Update: Thinktank asks May to extend the Brexit timeline
The Scottish Fraser of Allander Institute has warned against extending the Brexit timetable, which could be essential to the future prosperity of the United Kingdom.
He said that jobs and livelihoods could pose a risk in the case of a no-deal scenario, and urged the government to postpone the Article 50 deadline for withdrawal from the Union.