American soldiers Tuesday in Mosul, 2007. Photo: AP

WASHINGTON — The United States is stepping up its military campaign against Islamic State by sending hundreds more troops to assist Iraqi forces in an expected push on the city of Mosul, the militants’ largest stronghold, later this year.

U.S. Defense Secretary Ash Carter made the announcement on Monday during a visit to Baghdad, where he met U.S. commanders, as well as Iraqi Prime Minister Haider al-Abadi and Defence Minister Khaled al-Obeidi.

Most of the 560 additional troops will work out of Qayara air base, which Iraqi forces recaptured from ISOS and plan to use as a staging ground for an offensive to retake Mosul, Iraq’s second biggest city.

Government forces said on Saturday they had recovered the air base, about 40 miles from the northern city, with air support from the U.S.-led military coalition.

“With these additional U.S. forces I’m describing today, we’ll bring unique capability to the campaign and provide critical support to the Iraqi forces at a key moment in the fight,” Carter told a gathering of U.S. troops in Baghdad.

The new troops were “ready to come” and it would be a matter of “days and weeks, not months,” he said.

Abadi has pledged to retake Mosul by the end of the year.

However, there is still debate in Washington about the timing of a move on Mosul.

Some U.S. and allied military and intelligence officials warn that aside from its elite counter terrorism force, the Iraqi military is not ready to take on Islamic State militants in Mosul without significant assistance from the Kurdish peshmerga and Shi’a militias.

Moreover, Baghdad and Arbil, the capital of the autonomous Kurdish region, do not appear to have agreed on a plan for Mosul, and any significant participation by Kurdish or Shi’a forces in a Mosul campaign, one U.S. official said, “would create a whole new set of problems that the Abadi government is incapable of managing, or even mitigating.”

Separately, the Republican chairman of the House of Representatives Armed Services Committee said on Monday that President Obama must ask Congress for additional funds to pay for the deployment of more troops to Iraq, as Congress and the White House debate defense spending amid mandatory budget cuts.

Still, the latest U.S. force increase comes less than three months after Washington announced it would dispatch about 200 more soldiers to accompany Iraqi troops advancing towards Mosul.