NAIROBI, Kenya ? Gunmen attacked the African Union's main base in the capital, Mogadishu, on Thursday leading to an exchange of gunfire between militants and soldiers that left at least five militants dead, an official with the mission in Somalia said. Somali extremist group al-Shabab claimed responsibility for the attack and said they were targeting a Christmas party at the base, which also houses Western embassies and U.N. offices. At least eight men entered the AU base near the Mogadishu airport, AU Mission in...