While heralding what he said was the imminent defeat of Islamic State in Syria, Donald Trump has called on Europe to take back more than 800 foreign fighters captured in Syria and put them on trial.

Key points: US-backed fighters in Syria say they are poised to capture ISIS's last stronghold

US-backed fighters in Syria say they are poised to capture ISIS's last stronghold Most of the remaining IS fighters are said to be foreigners who travelled to Syria

Most of the remaining IS fighters are said to be foreigners who travelled to Syria Few governments want to repatriate fighters who could be hard to prosecute

The US President said on Saturday (local time) the militant group was "ready to fall", a day after signalling there would be "great announcements" about Syria over the next 24 hours.

"The United States is asking Britain, France, Germany and other European allies to take back over 800 ISIS fighters that we captured in Syria and put them on trial," he wrote on Twitter.

"The caliphate is ready to fall. The alternative is not a good one in that we will be forced to release them.

"The US does not want to watch as these ISIS fighters permeate Europe, which is where they are expected to go.

"We do so much, and spend so much — time for others to step up and do the job that they are so capable of doing.

"We are pulling back after 100% caliphate victory!"

US-backed fighters in Syria are poised to capture IS's last, tiny enclave on the Euphrates, according to battle commander Jiya Furat.

He said Syrian Democratic Forces (SDF) had cornered the remaining militants in a neighbourhood of Baghouz village near the Iraqi border, and they were under fire from all sides.

Syrian Democratic Forces (SDF) say they are close to defeating the remaining ISIS fighters. ( Reuters Rodi Said )

"In the coming few days, in a very short time, we will spread the good tidings to the world of the military end of Daesh," he said, using an Arabic name for IS.

Governments reluctant to repatriate IS fighters

Most of the fighters left in Baghouz are foreigners, the SDF has said, among the thousands drawn by IS leader Abu Bakr al-Baghdadi's promise of a new jihadist utopia straddling the Iraqi-Syrian border and expunging national borders.

In 2014, Baghdadi proclaimed himself caliph and set up a governing system with courts, a currency and flag, that at its height stretched from north-west Syria almost to Baghdad, encompassing 2 two million inhabitants.

Now all that remains, Jiya Furat said, was an encircled 700-square-metre pocket.

"Thousands of civilians are still trapped there as human shields," he said.

SDF spokesman Mustafa Bali said several militants had been caught trying to flee among civilians who were streaming out of the region. Others had handed themselves over.

Their fate, and that of their families, has befuddled foreign governments, with few ready to repatriate citizens who pledged allegiance to a group sworn to their destruction, but who might be hard to legally prosecute.

The SDF does not want to hold them indefinitely.

The fate of Baghdadi is also a mystery. He has led the group since 2010, when it was still an underground Al Qaeda offshoot in Iraq.

Its capacity then for strategic retreats in hard times, followed by rebounds when circumstances changed, has prompted numerous warnings that IS's military defeat will not end the threat it poses to the region.

US Army General Joseph Votel, who oversees US forces in the Middle East, said the end of the territorial caliphate would lead to a more dispersed, harder-to-detect network of fighters waging guerrilla warfare.

Reuters