Turkey’s military entered the key Syrian border town of Ras al Ain Saturday as its offensive against Kurdish fighters reached its fourth day despite rising international outcry and threats of US sanctions.

The Turkish government claimed its forces and allied Syrian rebels had captured the town center, but the Kurdish forces denied the town had fallen and said they were counter-attacking, Reuters reported.

The Turkish-based Syrian rebels entered the town after heavy shelling that the Kurdish troops said forced a tactical retreat in some parts of town. The Turkish government later posted photos of empty streets and Syrian rebels standing on Kurdish militia flags. But a Kurdish spokesman said a counter-attack started “and there are very fierce clashes now.”

The Observatory that keeps track of Syria’s civil war said 74 Kurdish-led SDF fighters have been killed since Wednesday as well as 49 Syrian opposition fighters backed by Turkey. The civilian toll on the Turkish side of the border rose to 18, while 21 civilians are dead on the Syrian side. The UN said 100,000 people had fled their homes, the Associated Press reported.

Turkey began the attack on the Kurdish YPG militia, which it sees as a terrorist group, after President Trump abruptly withdrew some US troops who had been backing Kurdish forces in the fight against Islamic State militants.

On Friday, some US special forces troops were caught in the middle of the action when Turkey shelled some positions near their post. The Pentagon said Turkey knew the US troops were in the area.