US forces to stay in Iraq 'as long as needed' to defeat IS: spokesman

"The main reason, after ISIS (Islamic State) is defeated militarily, is the stabilisation efforts and we still need to be there for that," US Colonel Sean Ryan said from Abu Dhabi.

But he said the number of US troops could go down once more NATO troops deploy to help train the Iraqi army. In February, NATO agreed to ramp up its presence in Iraq after Washington asked for assistance in stablising the war-torn country that has waged a costly battle against IS.

"Possibly, there could be a drawdown, it just depends on when NATO comes in and they help train the forces as well," Ryan said.

Iraq's prime minister Haidar al-Abadi delared victory over the militant group in December. 

The US has 5,200 troops in Iraq and 2,000 in Syria, where it backs the Kurdish-led Syrian Democratic Forces (SDF) to weed the group out of its last remaining desert pockets.

"We're starting to see a lot of collaboration between the SDF and ISF (Iraqi Security Forces) because it used to be that they would just come to the coalition, but now, we have them talking to each other as well," said Ryan.

Iraq's airforce began striking IS targets last year, with both the US and Syrian President Bashar al-Assad approving them.

But the campaign against the group on the Syrian side of the border has crawled to a slow after it planted hundreds of explosives, Ryan added. 

Ryan's comments come days after US officials notified Congress that it would not spend some $200 million that had been earmarked for Syria stabilisation programmes and would redirect the funds elsewhere. 

Agencies contributed to this report. 

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