Kurdish forces are trying to drive the militants out of Tel Abyad, in Syria’s Hassakah province, close to the Turkish border town of Akcakale.

The official said 3,337 Arab Syrians had crossed into Turkey in less than two days to avoid the clashes and bombing raids carried out against IS by a U.S.-led coalition.

The Syrians were being given biometric registration and health checks at Akcakale border crossing, the official added.

Turkey has already accepted 1.8 million people fleeing the bloodshed in neighbouring Syria, officially maintaining an open-border policy for refugees throughout the four-year-old civil war.

In recent months it has partly closed border gates on security grounds, however, prompting aid workers to raise concerns it is blocking people from escaping the fighting.

One aid worker said thousands of people seeking refuge in the last week had been turned back by Turkish border guards, many then heading for different destinations inside Syria.

“The impression we get is that Ankara is being extra careful,” the worker said. “They don’t want an influx of refugees just before an election.”

Campaigning climaxes this week ahead of parliamentary polls on Sunday, with the economic strain of housing refugees a sensitive issue.