LONDON (AFP) - Britain has insisted "much remains to be done" in fighting the Islamic State in Iraq and Syria (ISIS) group in Syria, amid reports on Thursday (Dec 20) 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 on Wednesday, referring to the militants.

"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."

Junior defence minister Tobias Ellwood was more blunt, retweeting a message from Mr Trump that the extremists 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."

Mr Trump declared on Wednesday that ISIS had been "beaten" in Syria and announced the pullout of American 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 ISIS.

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 Mr Trump announced it.