Turkish troops and their Syrian proxies gained ground Thursday in Ras al-Ain, a key border town where Kurdish fighters had been putting up stiff resistance, Syrian Observatory for Human Rights said.
Turkey launched a broad assault on Kurdish-controlled areas on October 9, after US troops pulled back from the border and started withdrawing from the northeast altogether.
"There have been intensive air strikes on Ras al-Ain over the past three days," Rami Abdel Rahman, the head of the Britain-based Observatory, said.
Turkish forces and the allies they use as a ground force had "taken about half of the town" by Thursday morning, he said.
Massively outgunned by the Turkish army and its airforce, Kurdish fighters from the Syrian Democratic Forces (SDF) quickly lost a long stretch of border when the assault was launched.
They organized a defense of Ras al-Ain however with a dense network of tunnels, berms and trenches that held off Turkish forces and their proxies for about a week.
An AFP correspondent on the Turkish side of the Ras al-Ain front line said the sound of gunfire and blasts from artillery and air strikes was constant.
Kurdish authorities in northeastern Syria accused Turkey of resorting to banned weapons such as napalm and white phosphorus munitions.
The administration said Turkey had resorted to their use because of unexpectedly stiff resistance by Kurdish fighters in Ras al-Ain.
"The Turkish aggression is using all available weapons against Ras al-Ain," the Kurdish statement said.
Turkey wants to create a 30-kilometer-deep buffer on the Syrian side of the border to keep Kurdish fighters at bay and set up a resettlement zone for some of the 3.6 million Syrian refugees living on its soil.
Turkish President Recep Tayyip Erdogan has so far ignored international pressure to halt the offensive, which has left dozens of civilians dead and displaced more than 300,000 people, according to the Observatory.
Abdel Rahman said the jump in the number of people forced to flee was due to a fresh wave of displacement over the past few days from areas around Tal Abyad and Kobane and in Hasakeh province.
Most displaced people tried to move in with relatives in safer areas, some were sleeping rough in orchards and others in some of the 40 schools that have been turned into emergency shelters, Abdel Rahman said.