Syria forces negotiating to free civilians from IS holdout

US-backed Syrian forces are negotiating to evacuate civilians from the Islamic State group's last redoubt which now faces "inevitable defeat", the international coalition said Thursday.

Hundreds of people including women and children were trucked out of the last patch of IS territory on Wednesday, but the Syrian Democratic Forces (SDF) said that a large number of civilians remained inside.

The Kurdish-led SDF, backed by the warplanes of the US-led coalition, have trapped IS fighters in less than half a square kilometre (a fifth of a square mile) in the village of Baghouz.

"Coalition forces, to include the US, continue to support the SDF as they negotiate having innocent civilians released and their fighters returned with the inevitable defeat in Baghouz," coalition spokesman Sean Ryan told AFP.

There was no immediate comment from the SDF, which has previously identified the remaining civilians as mostly wives and children of IS fighters.

Thousands of people -- mostly women and children related to IS members -- have streamed out of Baghouz in recent weeks.

The Syrian Observatory for Human Rights, a Britain-based war monitor, said Wednesday that there were negotiations "for the surrender of the last IS fighters".

It said there were "reports of a deal" but the details were unclear.

At the height of its rule, IS imposed its brutal interpretation of Islamic law on a territory roughly the size of Britain.

But the militants have since lost almost all their territory and hundreds of foreigners suspected of being IS fighters, as well as re