US troops are being withdrawn from Syria, after President Donald Trump said the ISIS group had been “defeated”, the Trump administration has announced.
However, the Pentagon said it was transitioning to the “next phase of the campaign” but did not give details.
Some 2,000 troops have helped rid much of north-eastern Syria of ISIS, but pockets of fighters remain.
It had been thought defense officials wanted to maintain a US presence to ensure ISIS did not rebuild.
There are also fears a US withdrawal will cede influence in Syria and the wider region to Russia and Iran.
Both the Pentagon and the WhiteHouse statement said the US had started “returning United States troops home as we transition to the next phase of this campaign”.
The Pentagon said it would not provide further details of what that next phase is “for force protection and operational security reasons”.
The White House said the US and its allies stood “ready to re-engage at all levels to defend American interests whenever necessary, and we will continue to work together to deny radical Islamist terrorists territory, funding, support and any means of infiltrating our borders”.
Israel said it had been told the US had “other ways to have influence in the area” but would “study the timeline [of the withdrawal], how it will be done and of course the implications for us”.
Russia’s Foreign Ministry spokeswoman Maria Zakharova said on state-controlled Channel One TV that the US decision could result in “genuine, real prospects for a political settlement” in Syria.
Pulling troops out of Syria had long been promised by President Trump.
The state department abruptly canceled its daily briefing on December 19 after the withdrawal was announced.
One of President Trump’s supporters, Republican Senator Lindsey Graham, who sits on the armed services committee, called it a “huge Obama-like mistake”.
In a series of tweets, Lindsey Graham said ISIS was “not defeated”, and warned withdrawing US troops puts “our allies, the Kurds, atrisk”.
This week Turkey said it was preparing to launch an operation against a Kurdish militia in northern Syria, which has been an ally of the US in its fight against ISIS.