Violent fighting is taking place around the Syrian border town of Ras al-Ain, as Turkish forces continue their military operations in northeastern Syria.
Turkey says it took the city, but the Kurdish Democratic Forces (SDF) run by the Kurds dispute that.
Turkey has also denied targeting US forces after the Pentagon said more troops in the west were attacked.
At least 30 civilians were reportedly killed and more than 200,000 people were reportedly displaced in four days of fighting.
The decision of President Donald Trump to withdraw American troops from the region has indeed triggered the Turkish incursion against the SDS, the main Western ally in the fight against the so-called Islamic State.
Turkey accuses the Kurds of being terrorists and claims to want to drive them out of a "security zone" inside Syria, where it plans to resettle more than three million Syrian refugees currently in Turkey.
One of the main concerns of the international community is the fate of thousands of alleged ISIS members, many of them foreign nationals, guarded by Kurdish-led forces in the region.
What is the last on the field?
The Turkish army and the homeless are engaged in violent clashes in Ras al-Ain. Warplanes went around the city, the city was hit by days of artillery bombardment and intense gunshots were heard.
Meanwhile, a spokesman for Turkey-backed rebels told the Reuters news agency that they had seized a strategic route between Tal Abyad and Ras al-Ain. and that 18 villages had been captured in advance.
On Friday, the Pentagon said that its base near the city of Kobane, in northern Syria – which was not part of the US withdrawal and where Turkey knew that US forces were present – had seen shells fired from Turkish positions. There was no injury.
Turkey said it had reacted to firing from the region and that it had stopped bombing after being informed by the United States.
The homeless are facing numerous Turkish land and air assaults along a stretch of the border between Turkey and Syria, some 120 km long, correspondents said.
On the fourth day of fighting, 74 SDF fighters were killed, mainly in the Tal Abyad region, the UK-based Syrian Observatory for Human Rights (SOHR) said.
Meanwhile, 49 armed fighters of Syrian rebels supported by Turkey and participating in the Turkish offensive were also killed.
The Turkish army confirmed the first death of a Turkish soldier and said that three others had been injured.
What is the situation for civilians?
Most of the civilian deaths occurred in the Tal Abyad region, SOHR said. Dozens of people were also seriously injured. Humanitarian groups say no less than 450,000 people may be forced to move.
The fighting also forced the only public hospital in Tal Abyad to close.
On the Turkish side, at least five people, including a Syrian baby, were reportedly killed during a Kurdish bombardment in towns on the Turkish border.
Why is the offensive happening?
Kurdish leaders – whose militia fought against the United States to defeat the IS – accuse the United States of having stabbed them in the back after Trump gave Turkey fire green to penetrate into northeastern Syria.
Mr Trump now says that he wants the United States to negotiate a truce between the ally of NATO, Turkey and the Kurds. Turkish President Recep Tayyip Erdogan, however, said that the military operation would continue.
Erdogan said he wanted to create a "security zone" in northern Syria, rid of Kurdish militias that could also host Syrian refugees.
Many US and other Western countries have condemned this incursion. More and more pressure is being exerted in Washington for Turkey to stop.
President Trump briefly touched on the situation as he was preparing to attend a rally on Friday, stating, "We do not want them to kill a lot of people … if we have to use sanctions, we will do it. "
What are the fears about IS based on?
The homeless claim to detain more than 12,000 alleged ISI members in seven prisons, of which at least 4,000 are foreign nationals. The exact locations have not been revealed, but some would be close to the Turkish border.
Five ISIS members left a prison in Qamishli town on Friday after the Turkish bombings in the area, a Kurdish spokesman said.
Two camps, Roj and Ain Issa, gathering families of alleged ISI members are in the "safe zone".
On Friday, Kurdish-led authorities reported that discussions were underway on how to move Ain Issa's camp, which had been shelled.
Turkey has said it will take responsibility for the state prisoners it found during its offensive.
Meanwhile, ISIS has intensified its attacks in northern Syria, causing six deaths during a bombing in Qamishli town on Thursday.
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