The U.S. is likely to weigh options ranging from military assistance to direct strikes to drive a growing al-Qaida presence out of the coup-wracked African nation of Mali, a Pentagon official said Thursday.

"We cannot allow al-Qaeda to sit in an ungoverned space and have a sanctuary and impunity," said Michael Sheehan, the Defence Department's assistant secretary for special operations.

U.S. officials first must find ways to work with the post-coup government in Bamako to combat the militants, Sheehan said at the Aspen Security Forum.

"We have to accelerate that effort," he said, now that al-Qaeda's African branch, known as al-Qaeda in the Islamic Maghreb, essentially has taken over Mali's northern region.

Mali's coup leaders have rejected U.S. assistance so far, but on Thursday said they would welcome a West African military intervention force to help recapture the north. (Rebecca Blackwell/Associated Press)

Mali's junta leaders handed power to an interim government after their revolt, but they still remain largely in control.

The coup leaders have rejected U.S. assistance so far, but on Thursday said they would welcome a West African military intervention force to help recapture the north — the first indication that the coup leaders would accept foreign troops.

The proposal for a 3,000-member military intervention force is still awaiting approval from the UN Security Council.

Sheehan said "all options would be considered for what is a looming threat," including strikes on the militants.

"What we will do with Mali, I can't speculate, but I think you can look at the whole range of things that have been successful in partnership with (other) governments, and perhaps operating in ungoverned space," Sheehan said.

Sheehan added that the U.S. is discussing the situation with U.S. allies France and Britain, who are equally concerned about al-Qaeda's spread.

Any next steps by the U.S. will be negotiated first by the American ambassador on the ground, added a senior military official, speaking on condition of anonymity because of the sensitivity of any such negotiations.

U.S. special operations forces have had an episodic training presence in Mali. Three special operations troops who were off duty were killed in a car crash, together with three local women, the day after the coup.

They had been part of a small training force there at the invitation of the last government, a second U.S. military official explained. He spoke on condition of anonymity because he was not authorized to speak about the program publicly.