BASE ELMENDORF-RICHARDSON, Alaska (REUTERS) - President Donald Trump told American troops on Thursday (Feb 28) that US-backed forces in Syria have retaken 100 per cent of the territory once held by Islamic State in Iraq and Syria (ISIS) militants, contradicting the commander of the US-allied Syrian Democratic Forces, who said it would take another week.

"We just took over, you know, you kept hearing it was 90 per cent, 92 per cent, the caliphate in Syria. Now it's 100 per cent we just took over, 100 per cent caliphate," Trump told troops at Joint Base Elmendorf-Richardson during a refuelling stop in Alaska.

Earlier on Thursday, the commander of Syrian Democratic Forces, Mazloum Kobani, said in a video released to the news media that the SDF would be able to announce "the complete victory over Daesh (Islamic State) in a week".

Trump made his comments while talking to US troops in Alaska about the progress his administration has made in Afghanistan and the Middle East over the past two years. He stopped in Alaska on his way back from talks in Vietnam with North Korean leader Kim Jong Un.

The US president has been anxious to declare that ISIS has been driven out of all its territory since announcing in December that he would withdraw American forces from Syria, claiming they had succeeded in their mission to defeat the militant group.

While the United States has withdrawn some troops, Trump responded to criticism of his move by deciding to leave some 400 US troops in the country over the longer run: 200 to remain in the north-east as part of a multinational force and 200 to remain at an outpost in the southeast to counter Iranian influence.

The US president said on Feb 6 he expected a formal announcement the following week that coalition forces had recaptured all territory previously held by ISIS in Syria. That announcement has yet to be made.