Ahlu Sunna Waljama'a group have taken control of Guri'el district in central Somalia after heavy fighting with Al-shabaab group, witnesses said on Saturday.
Twelve people were killed in the recent clash between rival groups.
Pictures show that Al-Shabaab fighters arrived the capital Mogadishu and patrol the streets of the city.
Last Mod: 27 Aralık 2008, 18:53
Al Shabaab, which means youth in Arabic, seized Gurael, 370 km (230 miles) north of the capital Mogadishu on Dec. 6, after three days of fighting with a government-allied moderate Islamist group in the area.
Ahlu Sunna Waljamaa is a religious organization with no political ambitions, but al-Shebab is fighting for to rule Somalia and impose Sharia Law. It agreed with Western-backed interim government despite Shabaab rejected an agreement with secular ruling.
Locals said the moderate group ousted by al Shabaab three weeks ago had been regrouping and launched their attack on Saturday morning.
"I have counted 12 dead fighters lying in the alleys of Gurael," witness Ali Aden told Reuters. "Some of them were injured by a mortar that landed in the hospital. Others were hit by stray bullets," he added.
Al Shabaab and other more moderate Islamist groups control all of the south and centre of Somalia except Mogadishu and Baidoa, the seat of parliament.
A third of the Somalian population need emergency aid in a humanitarian crisis that has been described as one of the worst in the world.
Ethiopian troops, which have been propping up the government since 2006, are due to withdraw from Somalia by the end of this month.
Somalia's President Abdullahi Yusuf is expected to resign soon, bowing to pressure from western countries and regional leaders who accuse him of obstructing a peace process, aimed at including opposition groups in the country's government.
MP Abdirashid Irro, a close ally of President Yusuf, told the VOA Somali Service that Yusuf has decided to resign and will address the Parliament soon.
Somalia's ailing president, now in his 70s, is a former warlord who has held together a multi-clan parliament and government since coming to power in 2004.
Analysts assert Islamists must be included in peace talks with Somalia's government to ensure lasting peace in the chaotic country which has been without a central government for 17 years.