Washington (AFP) - The US military's top officer on Thursday called for deploying American advisers to Iraq's Anbar province to counter Islamic State jihadists, but said the Baghdad government must first arm local Sunni tribes.

General Martin Dempsey's comments marked the first time the American military openly endorsed sending advisers to the restive western province, where Iraqi government troops have suffered a string of setbacks at the hands of the IS group.

Due to recent IS gains, "we need to expand the train, advise and assist mission into al-Anbar province, but the precondition for that is that the government of Iraq is willing to arm the tribes," Dempsey told a news conference.

"By the way, we have positive indications that they (Iraqi government) are. But we haven't begun to do it yet."

The US military has sent about 600 advisers to Baghdad and Arbil in the north to assist Iraqi and Kurdish forces and coordinate US-led air raids against IS.

The advisers are not heading into combat with Iraqi or Kurdish units but working with senior officers in Baghdad and Arbil.

Dempsey made the remark after he was asked about recent US airdrops of aid to a Sunni tribe near al-Asad air base that was forced to flee their homes in Heet in the face of advancing IS militants.

"The Iraqi security forces in al-Anbar province are in defensive positions and would be unlikely to be able to respond to a request for assistance from the Abu Nimer tribe," he said.