DAMASCUS - The UN has expressed concern about the fate of some 200 families reportedly trapped in the last tiny area of Syria still held by the Islamic State group.

Human rights chief Michelle Bachelet said they were apparently being prevented from leaving by IS militants.

They were also being subjected to intense bombardment by US-led coalition and allied Syrian forces, she added.

On Tuesday evening, dozens of lorries reportedly arrived on the outskirts of the IS enclave to evacuate civilians.

The Syrian Observatory for Human Rights, a UK-based monitoring group, cited its sources as saying wives and children of militants would be taken to an undisclosed location as part of a deal with the coalition.

Earlier, it reported that a request by militants to be given safe passage to the opposition-held Syrian province of Idlib or neighbouring Iraq had been rejected by the US-backed Syrian Democratic Forces (SDF) alliance.

SDF spokesman Mustafa Bali appeared to dismiss such an idea on Tuesday morning, insisting the militants had "only two options - either they surrender or they will be killed in battle".

"We are working on secluding and evacuating civilians and then we will attack. This could happen soon," Mr Bali was quoted as saying by AFP news agency.

Five years ago, IS controlled 88,000 sq km (34,000 sq miles) of territory stretching from western Syria to eastern Iraq. It proclaimed the creation of a "caliphate", imposing its brutal rule on almost eight million people and generating billions of dollars from oil, extortion, robbery and kidnapping.

Now, an estimated 300 militants and hundreds of civilians are surrounded inside about 0.5 sq km (0.2 square miles) of land in the Baghuz area, which is in the Middle Euphrates River Valley, near the border with Iraq.(FA)