Near Baghouz (Syria) (AFP) - Hundreds of civilians streamed out of the Islamic State group's last Syrian stronghold Tuesday into territory held by US-backed forces battling to finish off the jihadists' dying "caliphate".

A total of 3,500 people exited the riverside village of Baghouz, including 500 jihadists who had surrendered, the US-backed Syrian Democratic Forces said.

Five SDF fighters were also freed, their spokesman Mustefa Bali said on Twitter.

IS seized large parts of Syria and neighbouring Iraq in 2014, declaring a "caliphate" there, but has since lost all but a patch on the banks of the Euphrates River near the Iraqi border.

At a screening point for new arrivals outside Baghouz, an AFP reporter saw hundreds of men, women and children.

Men sat on the ground, surrounded by members of the Kurdish-led SDF, while women clad from head to toe in black waited to be searched.

Among them was the widow of French jihadist Jean-Michel Clain, 38, who said her husband had been killed last month after his brother Fabien.

"The drone killed my brother-in-law and then the mortar killed my husband," Dorothee Maquere told AFP.

Fabien Clain, 41, had voiced an IS audio recording claiming responsibility for the November 2015 attacks in Paris, when IS jihadists slaughtered 129 people in coordinated operations.

Backed by air strikes from the US-led coalition, the SDF smashed their way into the jihadists' last remaining sliver at the weekend.

But they slowed down the offensive on Sunday over concerns for civilians trapped inside.

Bali on Monday night said 3,000 more people had been evacuated since Sunday.

An SDF official told AFP "hundreds" of IS fighters were among them.

- 'War injuries' -

The Syrian Observatory for Human Rights, a Britain-based war monitor, earlier said 280 IS fighters were among those who quit the pocket since Sunday.

Diehard jihadists are fiercely defending their last patch after the SDF and the US-led coalition resumed their offensive late Friday, following a two-week pause to allow for civilian evacuations.

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The Kurdish-led force pushed into Baghouz on Saturday.

On Monday night, an AFP correspondent near the front line saw black smoke billowing over the besieged pocket after an air strike.

The Observatory, which relies on a network of sources inside Syria, said artillery fire and air strikes continued into the night.

The mass outpouring of people from the dying "caliphate" has sparked a major humanitarian emergency, with an aid group saying 600 people arrived early Tuesday in one camp for non-combatants in northeast Syria.

Among those who arrived at the camp in Al-Hol, 10 people "needed urgent medical treatment because of shrapnel or war injuries", the International Relief Committee said. Six were sent to hospital.

Around 15,000 people reached Al-Hol from Baghouz between February 22 and March 1, the UN's humanitarian coordination office OCHA said on Monday.

- Dying days of 'caliphate' -

The new arrivals have pushed the camp's population to over 56,000, exacerbating already dire conditions at the crammed facility, it said.

After months under heavy bombardment and sometimes with very little to eat, many of those emerging from Baghouz are in poor physical and psychological health.

Around 90 people, mostly children under the age of five, have died en route or shortly after arriving at Al-Hol, OCHA said.

Syria's Kurds hold hundreds of foreign jihadists and IS sympathisers, whose governments have been reluctant to take them back.

A US judge on Monday rejected a request for expedited treatment of the case of an Alabama woman who joined IS in Syria but has asked to return home.

The government has declared that Hoda Muthana, 24, is not an American citizen, and has barred her from entry.

The jihadists are massively outnumbered in Baghouz and the SDF say they expect a victory within days.

The Kurdish-led forces launched their broad offensive on remaining IS strongholds in the Euphrates Valley six months ago.

The capture of Baghouz would mark the end of IS territorial control in the region and deal a death blow to the "caliphate".

At its peak more than four years ago, the IS proto-state was the size of the United Kingdom and ruled millions of people.

Syria's war has killed more than 360,000 people and displaced millions since it started in 2011 with the brutal repression of anti-government protests.