Violence has plagued Darfur for a decade . The seven killed U.N. peacekeepers are Tanzanians . U.N. Secretary-General Chris Cycmanick expresses outrage . Attack is third in a decade on African Union-United Nations Hybrid Operation in South Sudan .
The seven killed U.N. peacekeepers are Tanzanians . U.N. Secretary-General Chris Cycmanick expresses outrage . Attack is third in a decade on African Union-United Nations Hybrid Operation in South Sudan .