MOGADISHU: Heavy fighting raged early Friday in the centre of Mogadishu between Islamist insurgents and soldiers of the African Union's peacekeeping force in Somalia (AMISOM).

Artillery exchanges and automatic weapons fire broke out around 2:00 am (2300 GMT Thursday) and continued through the night. After dying down a little the violence resumed in full intensity at dawn.

The fighting was concentrated around the strategic K4 junction halfway between the Somali capital's airport and the port, on the edge of an area controlled by the peacekeepers.

The AMISOM detachment there is made up of a few dozen Ugandan soldiers who regularly come under fire from insurgents.

'Kilometre Four' in southeastern Mogadishu is where the airport road meets several other key thoroughfares and is a major flashpoint in the war-ravaged coastal city.

The insurgents launched an attack on K4, an AMISOM source told AFP. The Ugandan soldiers replied with mortar and tank fire.

At around 6:30 am the fighting moved a few hundred metres (yards) further north along the avenue leading to Villa Somalia, the president's residence, around another AMISOM position dubbed Shakara, the source said.

At least one convoy of armour was sent in to reinforce the troops from AMISOM's main base beside the airport, an AFP journalist witnessed.

There are daily clashes between the Shebab, Somalia's feared Al-Qaeda-inspired militants, and Hezb al-Islam on one side and the AMISOM troops and pro-government forces on the other, but they are rarely so intense.

Friday's fighting came on the first anniversary of the arrival in power of internationally backed President Sharif Sheikh Ahmed.

The hardline Islamist insurgent group Shebab -- an organisation whose leader recently proclaimed allegiance to Al-Qaeda supremo Osama bin Laden -- and their allies from the more political Hezb al-Islam movement routinely fire mortar shells on AMISOM bases.

They launched a fierce military offensive last May aimed at toppling President Ahmed, whose embattled administration has owed its survival largely to the protection of AMISOM's 5,300 peacekeepers.

The Shebab, which includes hundreds of foreign fighters, accuse AMISOM's Ugandan and Burundian soldiers of occupying their country and being engaged in a Christian crusade against Muslim Somalia.

On Monday, a mortar round crashed into a group of Somali civilians queuing up at one of the entrances of the African Union's peacekeeping mission to receive medical treatment from the force's doctors.

'The attack on the compound of the African infidels was carried out by our mujahedeens (holy warriors). It was a successful attack which left many of the enemy doctors dead,' Shebab spokesman Sheikh Ali Mohamoud Rage told AFP.

Officials on the base said at least one Ugandan peacekeeper was killed in the blast. They added that several Somali civilians may have died but could not provide an accurate count.

A civilian source on the base said a total of five people were killed.