US-backed Syrian forces say they are close to defeating Islamic State in its final scrap of territory in Baghouz

US-backed Syrian forces have said they are close to defeating Islamic State in its final scrap of territory in eastern Syria.

Mustafa Bali, the head of the media office of the Syrian Democratic Forces (SDF), said the battle at Baghouz is ongoing and clashes continue after an encampment was seized from the jihadists on Tuesday.

Hardened militant fighters had been mounting a last-stand defence of the Baghouz enclave, which is all that is left of Islamic State's self-proclaimed "caliphate" that once spanned a third of both Syria and Iraq.

"This is not a victory announcement, but a significant progress in the fight against Daesh," Mr Bali said on Twitter, using an Arabic acronym for Islamic State.

The SDF captured hundreds of wounded militants when it overran the camp on Tuesday, Mr Bali said. It also captured 157 mostly foreign fighters.

Asked by Reuters how long it would take to defeat the remaining jihadists, Mr Bali said he expected the operation to end "very soon".

Some remaining militants had fallen back to the bank of the nearby Euphrates River, he said.

"The battles are not yet over," he said. "Some of the terrorists have taken their children as human shields. There are intermittent clashes."

Islamic State's fighters and followers have been steadily forced back to Baghouz after years of retreats in the face of military campaigns by foreign and local forces.

The group's defeat at Baghouz will mark a milestone in the struggle against the jihadists, although adherents are still widely seen as a big security threat with a presence in remote territory and capable of mounting guerrilla attacks.

The capture of Baghouz will also mark a significant moment in the wider Syrian war, wiping out the foothold of one of the main combatants.

But in a rare interview in February, M16 boss Alex Younger expressed concern at describing military defeat as a victory.

“We are not triumphant because I think from triumphant you get to hubris," he said.

“The reality is this is a societal, generational problem that we face in the West and it can only be addressed at that level.

“So, of course, the military defeat of the ‘caliphate’ does not represent the end of the terrorist threat. You can’t use military force to kill an idea but you can use it to denigrate and disrupt the sharpest end of the problem.”

Diehard jihadists have been mounting a desperate defence of the camp at Baghouz, deploying suicide bombers and car bombs.

Over the past two months, more than 60,000 people have poured out of the dwindling enclave, nearly half of whom surrendered as Islamic State supporters, including some 5,000 fighters, according to the SDF.

Even facing defeat, Islamic State's propaganda machine still functions. An audio recording released overnight purported to carry a message from spokesman Abi al-Hassan al-Muhajer saying the group would stay strong and urged fresh attacks.

It has also put out a video from inside the Baghouz camp, showing fighters among bullet-pocked cars and lying on earth ramparts as they fired assault rifles.

The scarred landscape around them was littered with vehicles, makeshift shelters and debris and shaded by clouds of billowing smoke.

Against this scene, a man with a scarf wrapped around his head stood to declaim a message of defiance, a small group of women and toddlers to one side of him.

The US military has warned that Islamic State may still count tens of thousands of fighters, dispersed throughout Iraq and Syria, with enough leaders and resources to present a menacing insurgency.

The Pentagon's own internal watchdog released a report last month saying Islamic State remained an active insurgent group and was regenerating functions and capabilities more quickly in Iraq than in Syria.

"Absent sustained (counterterrorism) pressure, ISIS could likely resurge in Syria within six to 12 months and regain limited territory," the report said.