W.J. Hennigan
Tribune Washington Bureau

ALBUQUERQUE, N.M.: The Pentagon plans to send about 600 additional troops to Iraq to help launch a long-awaited offensive to retake Mosul in coming weeks, the most ambitious operation yet in the two-year military campaign against Islamic State.

The escalation, which was approved by the White House, suggests the challenges U.S.-backed Iraqi ground forces will face in assaulting a heavily defended major urban center that is Islamic State’s self-declared capital in Iraq and the largest city under its control.

An Iraqi victory in Mosul would effectively end Islamic State’s self-declared caliphate in Iraq. President Barack Obama would like to see the militants ejected or defeated in Iraq before he leaves office in January.

The Pentagon has about 6,000 troops, mostly operating as advisers and trainers, in Iraq. U.S.-led coalition warplanes based outside Iraq have carried out thousands of airstrikes since mid-2014.

Most of the new U.S. troops will be deployed to Qayyarah, an Iraqi airbase known as Q-West about 40 miles south of Mosul that has become a key staging base for the planned assault.

Some also will be deployed to the Al Asad base, further west in Anbar province, to help with logistics.

A small component of special-operations forces will be dispatched to help Iraqi commanders gather and analyze intelligence from the battlefield.

Lt. Gen. Stephen Townsend, commander of U.S. forces in Iraq, must give his approval for the advisers to accompany Iraqi troops at the battalion level, meaning they could operate closer to the front line. U.S. advisers thus far have been largely confined to Iraqi division headquarters.

Defense Secretary Ashton Carter told reporters traveling with him in Albuquerque on Wednesday that the Pentagon plans to send “approximately 600 troops.” A senior defense official said 615 troops.

Carter said they will help Iraqi security forces and Kurdish fighters to “isolate and collapse” Islamic State’s control over Mosul and “to protect and expand Iraqi security forces gains elsewhere.”

“The Iraqi security forces have the combat role and we’re in the support role, but I need to make clear: American forces combating ISIL are in harm’s way,” he said, using an acronym for Islamic State.

Carter said the Pentagon does not know if the militants plan to fight street by street for Mosul, as many have feared, or will abandon the city before the assault force, as has happened in several battles recently.

The offensive, first promised in early 2015, has been repeatedly postponed as Iraqi security forces focused on retraining and on pushing the militants from other cities and towns closer to Baghdad, the capital.