Stepping up its military campaign against ISIS, the United States will be sending hundreds more troops to assist Iraqi forces in a highly anticipated push on the city of Mosul, the ISIS’ 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 Defense Minister Khaled al-Obeidi.

Most of the 560 additional troops will work out of Qayara air base, which Iraqi forces recaptured from Islamic State militants 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 60 km (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. 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 counterterrorism force, the Iraqi military is not ready to take on ISIS militants in Mosul without significant assistance from the Kurdish Peshmerga and Shi’ite 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’ite 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.”