(CNN) -- A brazen, daylight suicide bombing on the African Union's peacekeeping mission in Somalia's capital has killed at least 21 people, mostly peacekeepers, the mission said Friday. The attack came days after U.S. special forces killed Saleh ali Saleh Nabhan, pictured, in southern Somalia. Suicide bombers, disguised in two U.N.-marked vehicles, Thursday rammed through the security gate of the mission's headquarters, which is attached to Mogadishu's airport. They detonated their explosives just as Somalia's transitional government and mission representatives concluded a high-level meeting inside the compound, said the African Union's special representative for Somalia, Nicolas Bwakira. The attack killed four Somali civilians and 17 Ugandan and Burundian soldiers, including the mission's second in command, Burundian Maj. Gen. Juvenal Niyonguruza, he said.
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Seventeen soldiers, four civilians killed in attack on African Union base
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Bombing was carried out by militants driving vehicles bearing U.N. logos
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Al-Shabaab, the Islamist militia with ties to al Qaeda, claimed responsibility
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Strike came days after U.S. special forces killed a senior al Qaeda operative
The peacekeeping force is charged with protecting key government and strategic installations in @placeholder, including the port, airport and presidential palace.