MOGADISHU: Somalia's president was holed up in his compound and residents were fleeing Mogadishu Thursday, as hardline Islamist insurgents prepared their bid to seize power.

Radical opposition leader Sheikh Hassan Dahir Aweys urged his former Islamist ally President Sharif Sheikh Ahmed to leave office, as warring factions regrouped ahead of an expected final battle.

Insurgents have been redeploying forces from across the country to launch an unprecedented offensive, while Ugandan and Burundian African Union peacekeepers held the fort for Sharif's beleaguered administration.

"We know they have deployed many militants and are getting ready for their final attack but they will never win," Somali government security officer Colonel Ahmed Dahir told AFP in Mogadishu.

Sharif, who was elected Somalia's president in January and received international backing, has not been able to build up his own security forces and his authority appeared to hang by a thread after days of fighting in the capital that killed dozens and wounded hundreds.

Government forces backed by AU peacekeepers controlled nothing in the capital but the presidential compound, a handful of other government institutions in adjacent buildings, and the airport and seaport, witnesses said.

The 4,000-strong AU contingent's spokesman said he was confident his forces could hold off the Islamist-led insurgency and predicted that their stance against the government would earn them popular disaffection.

"Their intention is clear, they don't want peace and violence is their way of life. But they will not succeed, because the solution for peace in Somalia lies in having everybody on board through dialogue and not through violence," Major Bahuko Barigye told AFP.

After 18 years of almost uninterrupted civil conflict and more than two years of a brutal insurgency sparked by Ethiopia's 2006 invasion, Mogadishu has already been emptied of hundreds of thousands of its inhabitants.

But residents continued to flee Thursday, fearing that a fresh insurgent onslaught would be met by a barrage of artillery fire from AU and government forces hunkering down in a last handful of fortified pockets.

"There is no hope for peace in Mogadishu, we see that Islamists are planning attacks against the presidential palace and I saw the African peacekeepers deploying fresh troops and heavy artillery," said one resident, Farah Sahal.

"We have only one option and that is to flee from our house before it is too late," he told AFP as he packed a few modest belongings.

The International Committee of the Red Cross said in a statement that "thousands of people have fled their homes in search of shelter and security" over the past few days.

Hardline insurgents remained determined to topple Sharif's fledgling administration despite failing to go all the way with their initial offensive last week.

The insurgent forces consist mainly of the Shebab movement, a hardline group whose leaders are suspected of links to Al-Qaeda, and Hezb al-Islamiya, another armed organisation loyal to Sheikh Aweys.

"The purpose of this war is to protect a country and its religion from invading Christian forces and their Somali stooges. We will die for that," Shebab commander Sheikh Mohamed Ayyub told AFP.