The U.N. Security Council on Friday gave the green light to a new African Union force in Somalia that is meant to take on the Islamist armed group al-Shabab, with the soldiers due to deploy in January.

The resolution was adopted by 14 of the council's 15 member states, while the United States abstained due to reservations about funding.

It provides for the replacement of the African Union Transition Mission in Somalia, whose mandate ends on Dec. 31, by the African Union Support and Stabilization Mission in Somalia (AUSSOM).

Somalia is one of the world's poorest countries, enduring decades of civil war, a bloody insurgency by the al-Qaida-linked al-Shabab and frequent climate disasters.

Representatives from Somalia and its western neighbor Ethiopia were invited to participate in the council's meeting, although they were not allowed to vote.

"We emphasize that the current AUSSOM troops allocations are completed through bilateral agreements," said the Somali representative, adding 11,000 troops were currently pledged.

On Monday, Egypt's foreign minister announced his country would take part in the new force.

Tensions flared in the Horn of Africa after Ethiopia signed a maritime deal in January with the breakaway region of Somaliland, pushing Mogadishu closer to Addis Ababa's regional rival Cairo.

This month, Turkey brokered a deal to end the nearly yearlong bitter dispute between Somalia and Ethiopia, although Ethiopian troops would not be involved in the new AU force.

Burundi will not be taking part in the new force either, a Burundian military source told AFP on the condition of anonymity.

The text adopted by the U.N. Security Council provides for the possibility of using a mechanism that it created last year, under which an African force deployed with the green light of the U.N. can be up to 75% financed by the U.N.

"In our view, the conditions have not been met for immediate transition to application of" that measure, U.S. representative Dorothy Shea said, justifying her country's abstention.