US President Donald Trump on Thursday (December 20th) declared victory over the "Islamic State of Iraq and Syria" (ISIS) in Syria and abruptly ordered the withdrawal of US ground troops from the country, AFP reported.

"We have won against ISIS," Trump said in a short video posted on Twitter.

"We have beaten them and we have beaten them badly. We have taken back the land. And now it is time for our troops to come back home."

A US official told AFP that Trump's decision was finalized Tuesday.

"Full withdrawal, all means all," the official said when asked if the troops would be pulled from across Syria.

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

US-backed Syrian Kurdish forces said Thursday they will keep fighting ISIS in eastern Syria.

"The Hajin battle continues," said Mustafa Bali, a spokesman for the Syrian Democratic Forces (SDF), referring to the main front against ISIS in the Euphrates Valley.

"The US decision is just a decision and does not yet affect the situation on the ground," Bali said.

According to the Syrian Observatory for Human Rights, fighting was ongoing on Thursday.

Britain and France said on Thursday they remained committed to the fight against ISIS in Syria.

"The global coalition against ISIS has made huge progress, but much remains to be done and we must not lose sight of the threat they pose," British Prime Minister Theresa May's spokesman said.

"Even without territory, ISIS will remain a threat."

"We remain committed to the global coalition and the campaign to deny ISIS territory and ensure its enduring defeat, working alongside our critical regional partners in Syria and beyond."

"For now of course we remain in Syria," France's European Affairs Minister Nathalie Loiseau said on CNews television.

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