Abdi Hassan Awale Qeidid on Tuesday said he had crossed over from the US-backed Alliance for the Restoration of Peace and Counter-Terrorism (ARPCT) to the Joint Islamic Courts on advice of his elders from his Sa'ad sub-clan in order to avoid further bloodshed.
"I am no longer a member of the ARPCT and I quit that alliance immediately.
"I have left the alliance because of requests from elders and other civil society members from my Sa'ad sub-clan."
His abrupt exit leave Musa Sudi Yalahow, Bashir Raghe Shirar and Omar Muhamoud Finnish as the only faction chiefs still holed up in northern Mogadishu under the protection of the Abgal sub-clan and still vowing to fight on.
Qeidid, a former Somali police commissioner during the government of Mohamed Siad Barre, the former president who was toppled in 1991, was the commander in charge of the Afgoi belt, about 30km south of Mogadishu.
"Since the formation of ARPCT, Mogadishu has been a centre of a military crisis that has led to the needless death of hundreds of people, therefore I decide to quit the alliance to build on the gains of the Islamic tribunals and give peace a chance," he said.
Since the clashes erupted in Mogadishu in February, nearly 350 people have been killed and more than 2,000 others wounded, many of them civilians.
Washington's concerns over the rising power of Islamic radicals in Somalia manifested themselves in February when it helped the creation of the heavily-funded ARPCT, giving the alliance cash and intelligence support to hunt down extremists allegedly hiding in Somalia.
The Islamic courts have increasingly won support from the battle-weary Somalis owing to their slow but steady success in the restoration of order under their control.