Somali Islamist group Hizbu Islam is this week set to announce that it has joined the ranks of rival militia group al-Shabaab, a union that may pose a bigger challenge for the country's weak transitional government.
Sources say that al-Shabaab militants are already taking over positions held by Hizbu Islam in the capital Mogadishu.
The hardliner leader of Hizbu Islam, Sheikh Hassan Dahir Aweys, is early this week expected to confirm the development, according to reports.
If confirmed, the combined militias may pose a stiff challenge to the government which has been struggling to establish itself with the support of African Union peacekeepers.
Last week, the transitional government claimed that it now controlled more than half of the capital, although analysts say its influence over the city is extremely limited.
"There are vast areas of Mogadishu, over 55 per cent, which is controlled, along with the [AU Mission] Amisom forces, by the Somali army, the transitional government forces," Information and Telecommunications minister Abdulkareem Hassan Jama told a news conference at the UN headquarters.
Yield to pressure
"Many articles that you read say that the government only controls a few blocks and it could not survive without the help of Amisom," he said.
The United Nations is this week expected to pass a resolution that will allow the AU Mission to increase the number of peacekeepers from 8,000 to 12,000 troops.
According to popular Mogadishu broadcaster Shebelle, Sheik Aweys and his closest lieutenants will be rewarded with top positions in the bigger and far more radical al-Shabaab movement.
Al-Shabaab claims to control large swathes of the war-torn country, and has imposed strict Sharia law in those areas that are under it.
There had been speculation that Hizbu Islam would be forced to yield to pressure from al-Shabaab after the latter group's fighters captured Hizbu positions and advanced on others.
The latest Hizbu Islam surrender occurred on Saturday at Luq town, some 340 kilometres southwest of Mogadishu.