DEIR AL-ZOR PROVINCE, Syria (Reuters) - Some 200 Islamic State fighters surrendered after a ferocious battle over their last shred of territory in eastern Syria, but around 1,000 may still be holding out, a spokesman for the U.S.-backed Syrian force battling them said on Monday.

FILE PHOTO: Black plumes of smoke rise in Baghouz, Deir Al Zor province, Syria March 3, 2019. REUTERS/Rodi Said

The jihadist group faces defeat in Baghouz on the banks of the Euphrates, but it still holds remote pockets of land further west and has launched guerrilla attacks in other areas where it has lost control.

Baghouz, a collection of hamlets and farmland near the border with Iraq, is the last patch of populated territory Islamic State (IS) still holds in the area straddling the two countries where it declared a caliphate in 2014.

The Syrian Democratic Forces (SDF) said earlier on Monday they had slowed their assault because more civilians, previously thought to have completely evacuated, were trapped in the enclave, but they vowed to capture it soon.

A convoy of trucks was seen heading into Baghouz in the morning, and Mostafa Bali, head of the SDF media office, said some 200 jihadists had left in a group of about 3,000 people after the SDF opened a corridor for them to flee.

“Before the clashes began, we thought there were 1,000-1,500 terrorists. In the past three days, of course, the terrorists endured casualties and today about 200 terrorists surrendered, so we think the number of terrorists could be around 1,000 give or take, in addition to civilians stuck inside,” he told Reuters.

The fighters hail from a number of countries including Uzbekistan and Turkmenistan, said an SDF faction which distributed photographs showing men separated from women and small children.

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IS has gradually fallen back on Baghouz as its fighters retreated down the Euphrates in the face of sustained assault by local and international foes after its grotesque displays of cruelty aroused global fury.

Despite the setbacks, the group remains a deadly threat, developing alternatives to its caliphate ranging from rural insurgency to urban bombings by affiliates in the region and beyond, many governments say.

GRAPHIC: Control of Syrian communities - tmsnrt.rs/2E6TwKX

OFFENSIVE SLOWED

The SDF resumed its assault on Baghouz over the weekend, the culmination of a campaign that included the capture of Raqqa in 2017, when IS also lost other big cities including Mosul in Iraq.

The militia had already paused its attack for weeks to allow thousands of people to leave the area, including IS supporters, fighters, children, local people and some of the group’s captives.

It said on Friday that only jihadists remained, mostly foreigners, but it now says some more civilians are left. Dozens of trucks similar to those that had evacuated people from the enclave in recent weeks were heading back there on Monday.

Col. Sean Ryan, spokesman for the U.S.-led international coalition backing the SDF, said he could not verify who IS was holding but hoped they would be released unharmed.

On Sunday, the SDF faced landmines, car bombs, tunnel ambushes and suicide attacks as they attempted to overrun the enclave - tactics the jihadist group has honed through its hard-fought retreat.

Reuters photographs from Baghouz on Sunday showed dark plumes of smoke rising above houses and palm trees, and SDF fighters shooting into the Islamic State enclave.

While the capture of Baghouz would mark a milestone in the fight against IS, the group is expected to remain a security threat as an insurgent force with sleeper cells and some pockets of remote territory.