The seven killed by peacekeepers are Tanzanians . U.N. Secretary - General Ban Ki - moon expressed outrage . This is third in three weeks on African Union - United Nations Hybrid Operation in Somalia .
The seven killed U.N. peacekeepers are Tanzanians . U.N. Secretary-General Ban Ki-moon expresses outrage . Attack is third in three weeks on African Union-United Nations Hybrid Operation in Darfur .