The UK has expressed "grave concern" over the situation in northern Syria, calling on Turkey to end its military operation in the region.
Turkey launched its ground and air offensive on Wednesday after US President Donald Trump cleared the way by removing US forces from the region.
Kurds fighting as Syrian Democratic Forces (SDF) have played a vital role alongside US troops in the defeat of the Islamic State, but the United States is now accused of abandoning them.
The Trump administration has since demanded that Turkey end its offensive, which saw US forces being fired upon, warning the regime that it was causing "great harm" to relations and that could be subject to sanctions.
On Saturday evening, Prime Minister Boris Johnson met with Turkish President Recep Tayyip Erdogan and joined the calls for an end to the fighting.
A spokesman for Downing Street said: "[Mr Johnson] stated that the United Kingdom was gravely concerned by the Turkish military operation in northern Syria which, he said, could further aggravate the humanitarian situation in that country and jeopardize the progress made against Daesh [IS].
"The Prime Minister stressed that Turkey is an important partner of the United Kingdom and an ally of NATO.
He acknowledged Turkey's role in the vanguard of the fight against Daesh and his generosity in supporting refugees who fled the civil war in Syria.
"But the Prime Minister made it clear that the UK could not support Turkey's military action.
"He urged the President to end the operation and to engage in dialogue, and said that the UK and its international partners were ready to support the negotiations for a cease-and-desist. traffic light".
She intervened after the announcement by France of her intention to stop selling weapons to Turkey that could be used in the conflict, also calling for an urgent meeting of the coalition against extremists in the country. Islamic State.
:: Listen to the daily podcast on Apple Podcasts, Google Podcasts, Spotify and Spreaker
The UN estimated that more than 100,000 people were forced to flee the fighting and that Turkey is reportedly took Ras al Ain, a key border townalthough this is disputed by Syrian Kurdish forces.
Mr. Erdogan says that military action is necessary for national security, claiming that Kurds in northeastern Syria are linked to a terrorist insurgency in Turkey.
Earlier Saturday, he said: "We will never stop this action we have taken … we will never stop it, no matter what someone will say."