U.S. forces already advising Iraqi forces in Anbar province

General Martin Dempsey, chairman of the Joint Chiefs of Staff, said a small group of advisers had already established themselves in a preliminary fashion at Ain al-Asad air base in the province, much of which is controlled by the militant Islamist group.

They would also eventually start training the Iraqi army's seventh division, which suffered major setbacks during the Islamic State's advances across the country this summer.

"We have a train, advise and assist team in al-Asad air base," Dempsey said in an interview conducted on Saturday. "There's enough there that are already working with the seventh division to help them plan and help them understand the threat, to advise them on how to consolidate their forces."

President Barack Obama's administration announced on Nov. 7 it would send up to 1,500 more U.S. troops to Iraq, widening its advising mission and initiating training of Baghdad's forces. At the time, officials suggested the expansion would take weeks to get underway.

The seventh division's ability and willingness to engage Sunni militant forces in Anbar could be vital to any sustained offensive to reverse Islamic State's gains. The jihadist group took Anbar's two main cities, Falluja and Ramadi, several months before it overran much of the rest of the country, often facing little resistance from Iraqi government forces.

TIES WITH SUNNI TRIBES CRITICAL 

An aide to Dempsey said the U.S. troops, who numbered just under 50, were also already helping the seventh division as Iraq starts to build ties with Sunni Muslim tribes in the region.

The goal is to create a bridging force of thousands of Sunni tribesmen before Iraq's Shi'ite-led government creates a "National Guard", decentralizing power from Baghdad.

The official said the U.S. training operation at al-Asad was expected to get underway this year.

Iraq's army has been burdened by a legacy of sectarianism in Anbar, whose dominant Sunni population resented former Prime Minister Nuri al-Maliki's Shi'ite majority government and were incensed when he ordered troops to clear a protest camp in Ramadi in late December 2013.

The ensuing Sunni tribal revolt prompted the entrance of Islamic State into Falluja and Ramadi, where U.S. troops had met fierce resistance from Sunni insurgents including al Qaeda during their occupation of Iraq after the 2003 invasion that overthrew Saddam Hussein.

Dempsey described the American troops at the base as the preliminary group that would establish the training site at al Asad. "There's an adequate contingent there that can both protect itself and advise but it will need to be expanded slightly ... in order to establish the training base," he said.