Seven United Nations peacekeepers were killed Saturday in Sudan's troubled Darfur region when gunmen ambushed their group.
The assault marked the single deadliest attack on the joint African Union-U.N. peacekeeping force in its five-year history.
The force, known as UNAMID, said the team came under heavy fire from a large unidentified group. A spokesman said the "extended firefight" took place some 25 kilometers west of the town of Khor Abeche in an area where Tanzanian troops are in charge of peacekeeping.
At least 17 other peacekeepers were injured in the attack, two of them female.
In a statement, U.N. Secretary-General Ban Ki-moon said he was "outraged" by the attack.
The peacekeeping force, established to protect civilians in Darfur, has at least 20,000 military and police officers. But peace efforts have failed to end the conflict in Darfur, where rebels took up arms 10 years ago against the Sudanese government, accusing it of discrimination.
The violence, which the U.N. estimates has killed more than 300,000 people, has fallen from its peak between 2003 and 2005. But it has been worsening again this year as government forces, rebels and Arab tribes are now fighting each other over land and resources.
In April, another attack in Darfur killed a Nigerian peacekeeper.