The UN Security Council will soon agree to authorize 4,000 more troops to boost the African force battling resurgent Shebab rebels in Somalia, diplomats said Wednesday.
The council is likely to allow a new upper limit of about 22,000 troops for the African Union force amid mounting warnings over the Shebab militant threat after the Nairobi shopping mall attack last month.
UN Deputy Secretary-General Jan Eliasson told the council that advances made by the African force with the Somali army had "ground to a halt" because it lacked a sufficient number of troops.
The AU force, officially known as AMISOM, and the Somali army have pushed the fighters out of the capital Mogadishu and other major cities over the past 18 months.
But the Shebab have regrouped and staged spectacular attacks, such as the Westgate Mall strike in Nairobi on September 17 in which 67 people died.
Suicide bombers have also inflicted major casualties in Mogadishu.
Shebab "is mobile and is training and recruiting substantial numbers of frustrated, unemployed young men," Eliasson told a Security Council meeting on Somalia and efforts to support the country's interim government.
Eliasson reaffirmed a call by UN leader Ban Ki-moon and the African Union for "a significant temporary boost" to AMISOM's numbers.
The African Union has said it needs an extra 2,550 infantry troops and 1,800 support forces.
Ban said in a recent report to the Security Council that there is an urgent need to reinforce AMISOM to move into southern Somalia to "deny Shebab the opportunity to raise resources and to forcefully recruit and train personnel."
Britain is drawing up a resolution on increasing the force which is expected to be voted by the Security Council in mid-November.
The resolution would allow for an increase of about 4,000 troops to allow an upper limit for AMISOM of about 22,000, UN diplomats said.
AMISOM, first deployed in 2007, is a unique military operation as it is run by the African Union, but with a UN mandate. Most of its financing comes from the European Union and other international donors.
Because it does not have a UN peacekeeping mandate, the force -- made up of troops from Uganda, Burundi, Djibouti, Kenya and Uganda -- can carry out offensive operations against the Shebab.
But critics warn of the mission's heavy cost and bureaucracy, and many international powers are reluctant to repeat the mission in other conflicts.