Officials with the Kurdish-led administration in northern Syria said 785 foreigners affiliated with ISIS managed to escape a camp where they were being held following Turkish shelling on Sunday.

In an apparent reference to Turkish-backed Syrian rebels, the administration said in a statement that “mercenaries” had  attacked the camp where members of the Islamic State in Iraq and Syria in turn attacked camp guards and opened the 

The news comes a day after Turkey’s military said it captured a key Syrian border town under heavy bombardment in its most significant gain since an offensive against Kurdish fighters began four days earlier, with no sign of relenting, despite mounting international criticism.

Turkish troops entered central Ras al-Ayn, according to Turkey’s Defence Ministry and a war monitor group. The ministry tweeted: “Ras al-Ayn’s residential centre has been taken under control through the successful operations in the east of Euphrates” River. It marked the biggest gain made by Turkey since the invasion began Wednesday.

The continued push by Turkey into Syria comes days after President Donald Trump cleared the way for Turkey’s air and ground offensive, pulling back U.S. forces and saying he wanted to stop getting involved with “endless wars.”

Trump’s decision drew swift bipartisan criticism that he was endangering regional stability and risking the lives of Syrian Kurdish allies who brought down ISIS in Syria. The Kurdish-led Syrian Democratic Forces was the main U.S. ally in the fight and lost 11,000 fighters in the nearly five-year battle against ISIS.

Turkish troops and allied Syrian opposition fighters have made gains recently, capturing several northern villages in fighting and bombardment that left dozens of people killed or wounded. The invasion also has raised concerns that IS might take advantage of the chaos and try to rise again after its defeat in Syria earlier this year.

Turkish President Recep Tayyip Erdogan said Friday that Turkey won’t stop until the Syrian Kurdish forces withdraw beyond a 32-kilometre line from the border.