Syrian Democratic Forces (SDF) backed by coalition warplanes tried Thursday (March 14th) to break the last defences of "Islamic State of Iraq and Syria" (ISIS) fighters making a suicidal last stand in Syria's Deir Ezzor, AFP reported.

The SDF have since Sunday rained fire on the enclave in al-Baghouz. But hardliners still inside are putting up fierce resistance, hiding underground from coalition airstrikes and unleashing suicide bombers on advancing forces.

"There is progress but it is slow as the area is narrow," said Jiaker Amed, a spokesman for the Kurdish People's Protection Units (YPG).

"Those who stayed inside are mostly suicide bombers blowing themselves up, which is impeding the advance," he said, adding that "they are using below-ground tactics", hunkering in tunnels and trenches.

Since the offensive resumed Sunday, 3,000 ISIS members have surrendered, SDF spokesman Mustafa Bali has said.

Save the Children said Thursday more than 3,500 foreign children from more than 30 countries were estimated to be living in camps in north-east Syria.

Of these, over 2,000 are aged less than five years old, the charity said.