Britain has insisted 'much remains to be done' in fighting the Islamic State group in Syria, amid reports on Thursday that it was not given prior warning of President Donald Trump's decision to pull out US ground troops.

'The global coalition against Daesh has made huge progress,' said a government statement issued late Wednesday, referring to the jihadists.

'Since military operations began, the coalition and its partners in Syria and Iraq have recaptured the vast majority of Daesh territory and important advances have been made in recent days in the last area of eastern Syria which Daesh has occupied. 

'But much remains to be done and we must not lose sight of the threat they pose. Even without territory, Daesh will remain a threat.'

UK junior defence minister Tobias Ellwood was more blunt, retweeting a message from Trump that the jihadists had been defeated in Syria with the words: 'I strongly disagree. It has morphed into other forms of extremism and the threat is very much alive.'

Trump declared on Wednesday that IS had been 'beaten' in Syria and announced the pullout of US ground forces from the war-ravaged nation.

Currently, about 2,000 US forces are in Syria, most of them on a train-and-advise mission to support local forces fighting IS.

The Pentagon refused to say what effect the troop withdrawal would have on air operations in Syria that have been ongoing since late 2014.

Britain takes part in the air strikes as part of an international coalition.

The statement from London said: 'We remain committed to the global coalition and the campaign to deny Daesh territory and ensure its enduring defeat, working alongside our critical regional partners in Syria and beyond.

'As the situation on the ground develops, we will continue to discuss how we achieve these aims with our coalition partners, including the US.'

The Times newspaper on Thursday reported that Britain had not been informed of the decision before Trump announced it.

Furthermore, France will maintain its participation in the coalition fighting Islamic State forces in Syria, government officials confirmed.

'For now of course we remain in Syria,' France's European Affairs Minister Nathalie Loiseau said on CNews television, adding 'the fight against terrorism is not over.'

'It's true that the coalition has made significant progress in Syria, but this fight continues, and we will continue it,'she said.

France has stationed fighter jets in Jordan and artillery along the Syrian border in Iraq as part of the US-led coalition, as well as an undisclosed number of special forces on the ground.

French Defence Minister Florence Parly said on Twitter Thursday that the group 'has not been wiped of the map, nor have its roots. We must definitively defeat the last pockets of this terrorist organisation,' she said.