US President Donald Trump appears to have prematurely claimed defeat against the Islamic State terror group's last bastion in Syria.

The White House announced that its territory in the nation had been "100%" eliminated, while the US president brandished a map to reporters apparently showing its destruction.

But it is understood the Kurdish-led Syrian Democratic Forces (SDF) are not yet ready to claim victory in IS's final stronghold of Baghouz.

SDF spokesman Mustafa Bali went on to say "heavy fighting continues" around Baghouz to finish off the remnants of IS "right now" - some two hours after the White House announcement.

Britain has supported an international coalition to destroy the group by delivering airstrikes on key targets with RAF jets and Reaper drones carrying out attacks, surveillance and reconnaissance.

British Army soldiers on the ground have also trained thousands of members of the Iraqi Security Services and provided Kurdish fighters with weaponry and ammunition.

Baghouz, which is on Syria's border with Iraq, is the last strip of territory left over from IS's so-called caliphate, which once stretched across swathes of both nations.

Mr Trump's press secretary Sarah Sanders had said he was briefed by acting defence secretary Patrick Shanahan, who travelled with him aboard Air Force One.

The president showed a map to reporters showing IS's apparent elimination, saying: "Here's Isis on Election Day. And here's Isis right now," with no red marks for territory remaining.

It is not the first time he has spoken prematurely on the matter. On Wednesday he said Baghouz would fall that night.

The president's latest claim was quickly disputed.

CNN's Ben Wedeman, who has been reporting from Baghouz, tweeted that airstrikes and heavy machine gun fire could be heard.

"I guess not everyone heard the White House statement re 100 percent elimination," he added.