A battle is under way for a key Syrian border town as Turkey presses its military assault against Kurdish fighters in the region.
But while Ankara said its forces had seized the centre of Ras al Ain this has been disputed by Syrian Kurdish forces.
The capture of the town would be Turkey’s most significant gain since its invasion began on Wednesday.
Ankara launched its ground and air offensive into northern Syria after Donald Trump cleared the way by pulling back American forces from the area, who had been fighting alongside Kurdish forces against Islamic State (IS).
Washington has subsequently demanded Turkey halt its offensive, which has seen American forces come under artillery fire, warning the regime that it was causing “great harm” to ties and could face sanctions.
There has been international condemnation of the offensive, with accusations of ethnic cleansing and fears about the humanitarian cost.
The UN has estimated more than 100,000 people have been forced to flee the fighting.
The UK’s Foreign Secretary Dominic Raab has said Turkey’s military assault weakens the fight against IS and risks deepening the plight of civilians in the war-ravaged region.
He argued that Ankara must show “maximum restraint” as the air and ground offensive enters its fourth day.
But Turkish President Recep Tayyip Erdogan has dismissed the mounting criticism insisting that Turkey “will not stop it, no matter what anyone says”.
Meanwhile, IS have moved to exploit the conflict, exploding a car bomb at a prison in the city of Hasaka in northeastern Syria, in a bid to breakout detained militants.
The blast forced Kurdish-led security forces to send reinforcements to prevent an escape.
Eerie, scary and virtually silent
Border being cleansed of Kurds
A Kurdish official has already warned that the Turkish offensive has weakened its ability to secure prisoners.
In Ras al Ain, one of two Syrian border towns targeted in the offensive, thick plumes of smoke could be seen amid the sound of gunfire and warplanes flying overhead.
It was reported to be quieter at Tel Abyad, the operation’s other main target some 75 miles (120km) to the west, with only occasional shelling heard.
Earlier, Turkish-backed Syrian rebels said they had cut the road which connects Ras al Ain and Tel Abyad and had captured 18 villages since the operation began.
The Turkish defence ministry tweeted: “Ras al Ain’s residential centre has been taken under control through the successful operations in the east of the Euphrates (river).”
But the Kurdish-led Syrian Democratic Forces (SDF) denied this and said while Turkish-backed forces had entered one neighbourhood, a counter-attack was under way.
Sky News foreign affairs editor Deborah Haynes, who is in Ceylanpinar, said Ras al Ain had been “a signficant focus of Turkish firepower”.
“In the past hour we’ve heard Turkish jets overhead. They are high up above us – we can’t see them, just hear them,” she added.
Erdogan: We will not stop Syria assault no matter what anyone says
Turkey claims to have killed 49 “terrorists” so far, while six civilians in Turkey and seven in Syria have also died.
Turkey says it aims to push back Syrian Kurdish forces, which it considers terrorists its links to a decades-long Kurdish insurgency within its own borders.
But the military action has raised concerns about the threat of a an IS resurgence.
The SDF was the main US ally in the fight against IS, losing 11,000 fighters in the nearly five-year battle against the extremists.