Diehard fighters from the Islamic State group and their families remained holed up in a last pocket, despite US President Donald Trump's claims that 100 percent of jihadist territory was retaken.

The Syrian Democratic Forces (SDF) evacuated several hundred people late Thursday from Baghouz, a hamlet by the Euphrates where the "caliphate" looks set to peter out.

"Many foreigners from various nationalities were among them," SDF spokesman Mustefa Bali told AFP without specifying which ones.

Up to several thousand people are thought to remain in a makeshift camp on the edge of Baghouz, the last dreg of a jihadist proto-state that was larger than Britain four years ago.

In remarks to US service members delivered in Alaska on his way back from Vietnam, Trump again jumped the gun on declaring victory over the jihadists.

"We just took over — you know, you kept hearing it was 90 percent, 92 percent — the caliphate in Syria. Now it's 100 percent. We just took over," he said.

That was contradicted by facts on the ground however and by officials from the SDF, which has been the main ground force ally of the anti-IS military coalition led by Washington.

Earlier on Thursday, another SDF spokesman, Adnan Afrin, said his force was waiting to complete evacuations from Baghouz before launching a final push to defeat the jihadists.

"We want the evacuation operations to finish as soon as possible so we can move to the next phase: an assault or the surrender" of the jihadists still inside, Afrin said.

Mazloum Kobani, the general commander of the Kurdish-led force, also said the epilogue of the operation against IS's Euphrates Valley heartland, launched in September last year, could drag on another week.

"In around one week, we will declare complete victory over IS," he said.

Kobani was speaking in a video released by the SDF's media office on Thursday of his visit to SDF fighters who were released after being held hostage for three weeks by IS.

The commander said that their safe release and that of other SDF force members apparently still held was a factor in slowing down operations against Baghouz.

The exodus from IS's last redoubt, where people have been besieged and starving for weeks, continued to generate epic scenes of mass displacement.

Almost every day, women veiled from head to toe, their arms loaded with scruffy children and bags containing their scant belongings, can be seen trudging through the countryside towards an SDF assembly point.

There are also some men among the evacuees, who get trucked to a screening centre and dispatched to camps or prisons.

The Kurdish-run camp of Al-Hol, which has received most new arrivals in recent days is completely overwhelmed.

Its population has soared past 50,000 and aid organisations fear dysentery and other diseases could break out.

The United Nations issued a statement on Thursday calling for urgent funding to help scale up the emergency response.

"More tents, food, non-food items, water and sanitation, health and protection services, as well as other emergency supplies are urgently needed," it said.

The US-led coalition on Thursday confirmed that notorious French jihadist Fabien Clain was killed in an air strike on Baghouz last week.

Clain gained notoriety after voicing an audio recording claiming responsibility for the November 2015 attacks in Paris, when IS gunmen slaughtered 129 people in coordinated attacks at restaurants and bars around the French capital.

The fate of the group's top leader, Iraq-born Abu Bakr al-Baghdadi, remains unknown however.

While the last remains of IS's statehood experiment are about to disappear, the group remains a potent force in both Syria and Iraq.

Since it lost major cities such as Mosul and Raqa to successive operations in 2017, IS has resumed the guerrilla warfare it waged before the "caliphate".

It carries out frequent attacks in areas from which it was expelled and the Pentagon has warned a major resurgence is likely if insufficient pressure is applied on the group in the coming months.