The U.N. Security Council will soon be asked to approve a Western-backed security force to combat the spreading terrorism threat in Mali, a senior European official said Wednesday.

The force would confront an African affiliate of al-Qaeda that has flourished in largely lawless northern Mali and that is expanding its reach.

The force would be made up of African troops primarily financed and possibly armed from outside, the official said. France, for example, is willing to provide unspecified logistical help.

The official, who spoke on the condition of anonymity because the proposal is not final, said its sponsors want the force approved in a matter of days or weeks.

“There is real urgency there,” the official said. “The terrorist threat is spreading.”

The United States has ruled out any direct military participation in Mali and has not publicly committed to arming or funding such a force.

Mali’s interim government has said that it would welcome about 3,300 troops from a 15-nation consortium known as the Economic Community of West African States.

“We do have growing concerns,” State Department spokeswoman Victoria Nuland said Wednesday.

The United States is “working closely to support the efforts of ECOWAS to further elaborate a robust peacekeeping plan with the new interim government of Mali,” Nuland said. “We’re prepared to support a well-thought-out plan in the Security Council when it comes forward but with ECOWAS very much in the lead.”

The White House has held a series of secret meetings in recent months to examine the threat posed by al-Qaeda’s franchise in North Africa and consider for the first time whether to prepare for unilateral strikes, U.S. officials told The Washington Post this week.

The deliberations reflect concern that al-Qaeda’s African affiliate has become more dangerous since gaining control of large pockets of territory and acquiring weapons from post-revolution Libya. The discussions predate the Sept. 11 attacks on U.S. compounds in Libya but gained urgency after the assaults there were linked to al-Qaeda in the Islamic Maghreb, or AQIM.

U.S. officials said the discussions have focused on ways to help regional militaries confront al-Qaeda but have also explored the possibility of direct U.S. intervention if the terrorist group continues operating unchecked.

The top State Department official for African affairs said Tuesday that AQIM and related militant groups in Mali “must be dealt with through security and military means.”

“Given the presence of terrorists and traffickers in Northern Mali, the United States supports the efforts of the government of Mali and the international community to prepare a military response as necessary, in accordance with international law,” said the official, Assistant Secretary of State Johnnie Carson. “Such a response should be well planned, managed, resourced, and coordinated.”

The European official said that unilateral U.S. action appears unlikely and that diplomatic efforts are focused on the peacekeeping force.

ECOWAS is unable to field an effective security force on its own, the European official said, so the proposed U.N.-authorized force would step in. The official said the size of the proposed force is under discussion among Britain, France, the United States and other nations.

“It has to be a rather robust force if you really want to rebalance the situation,” the official said.

“For many reasons, including political reasons, it has to be an African force,” strongly supported from outside, the official said. Sending soldiers or peacekeepers from former European colonial powers would be “unthinkable.”

AQIM is the most dangerous of the terrorism network’s affiliates and poses the strongest al-Qaeda threat to Europeans, the European official said.

The U.S. military commander for Africa has crisscrossed the region in recent weeks, making stops in Mauritania, Algeria and other countries that could become part of a peacekeeping force for Mali.

Army Gen. Carter F. Ham, chief of U.S. Africa Command, said Friday during a visit to Morocco that there “are no plans for U.S. direct military intervention” in Mali. But he and others have made clear that the United States is prepared to support counterterrorism or peacekeeping operations by other countries.