UNITED NATIONS (AP) — The U.N. called Tuesday on Sudan's government to identify those behind a deadly attack on the joint African Union-United Nations mission in Darfur over the weekend.

Seven Tanzanian peacekeepers were killed Saturday and another 17 people were wounded in the deadliest ever attack on the international force in Sudan's troubled western region.

U.N. spokesman Martin Nesirky said Tuesday that the peacekeepers were ambushed while on a routine patrol and were outnumbered four-to-one. The peacekeepers faced about 100 and 150 people on trucks mounted with anti-aircraft guns. One of the mission's trucks was stolen and three of its vehicles were damaged.

Nobody has claimed responsibility for the attack, which was the third on U.N. forces in the region in the last three weeks.

A February report by a U.N. panel of experts said that some armed opposition groups angry about the peacekeepers' presence have called them "a legitimate target."

Saturday's attack took place against a backdrop of escalating violence in Darfur. Inter-communal fighting among militias and clashes with government forces have increased in intensity and frequency since January, according to a report by Secretary-General Ban Ki-moon to the Security Council.

An estimated 300,000 people have been displaced in Darfur this year, more than the past two years combined, the report said. Access to civilians in conflict zones often remains constrained for aid workers, due to government restrictions, it said.

Ban recommend a one-year extension of the peacekeeping mission, which he called essential for protecting civilians and humanitarian workers, and implementing the 2011 Doha Document for Peace in Darfur.