Mogadishu  - At least four African Union peacekeepers were seriously injured and possibly killed in Mogadishu Friday when a roadside bomb blew up the truck they were travelling in, witnesses said.

"It was huge blast. The truck was totally destroyed - it was scattered into pieces," Ibrahim Dahir Salad, a tailor who witnessed the incident, told Deutsche Presse-Agentur dpa.

Salad said he saw four soldiers being carried away from the convoy, which was comprised of mainly Ugandan soldiers.

AU spokesman Major Bariyge Bahuko would only confirm the attack took place, saying that further details would be released at a Saturday press conference.

There are around 1,800 AU troops in Somalia, all from Uganda and Burundi. Some 8,000 troops are supposed to be policing the conflict-ridden nation, but other African states have yet to fulfil their pledges.

The militant group al-Shabaab, the armed wing of the Union of Islamic Courts, has vowed to step up attacks on foreign troops and civilians after a US airstrike killed its leader Aden Hashi Ayro in early May.

Ayro was believed to be al-Qaeda's top commander in the country.

The Union of Islamic Courts controlled Mogadishu for around six months in 2006 before being driven out by government and Ethiopian troops, sparking an insurgency.

Another bomb attack earlier this week saw three Ethiopian and two Somali soldiers killed.

Two Italian aid workers were also kidnapped this week, adding to the growing list of foreigners kidnapped or killed in recent months. One Kenyan and one British aid worker are also still being held.

However, Somali gunmen on Friday released Kenyan professor Moses Nyandusi Matundura, who was abducted in the capital city ten days previously.

"Moses now is in the university. He is safe and was well treated while he was held captive," one of his colleagues told dpa.

Somalia has been in a state of anarchy since the ouster of dictator Mohamed Siad Barre in 1991.

It has been without an effective central authority, leading to constant inter-clan clashes that have left thousands dead and around one million displaced. (dpa)