The African Union has condemned an assault on the organization's main base in Somalia by al-Shabab extremists that killed three AU soldiers and a civilian contractor.AMISOM, the AU mission in Somalia, issued a statement Thursday saying that the four had been killed in a gunfight as soldiers tried to repel the attack by eight militant gunmen."The terrorists, some of whom were disguised in Somali National Army (SNA) uniforms, breached the base camp around lunch hour and attempted to gain access to critical infrastructure, during which five of them were killed and three others captured," the African Union statement said."Our forces shot dead three of them, two detonated themselves near a fuel depot, and the three are believed to have escaped," AMISOM spokesman Col. Ali Aden Houmed told The Associated Press.By way of background, the AP says: