"On occasion, this discontent has also manifested itself in incidents of direct attacks on UNAMID staff and premises, although some of these incidents — especially those of carjacking and kidnapping of UNAMID peacekeepers — appear to have an overtly criminal intent of financial gain for the perpetrators," the report said.
Darfur has been gripped by bloodshed since 2003 when rebels took up arms against the government in Khartoum. More than 300,000 people have been killed in the conflict. The International Criminal Court indicted Sudanese President Omar al-Bashir in 2009 on genocide and war crimes charges over the fighting in Darfur. The country split into Sudan and South Sudan in 2011.
Unrest continues in the region. About 300,000 people have fled fighting throughout Darfur in the first five months of this year, the U.N. has said.
"The mission condemns in the strongest possible terms those responsible for this heinous attack on our peacekeepers," said Mohamed Ibn Chambas, a joint special representative of the force. "The perpetrators should be on notice that they will be pursued for this crime and gross violation of international humanitarian law."
More than 100 U.N. peacekeepers were killed last year alone on duty in the Darfur and Abyei regions of Sudan, Congo, Ivory Coast and other countries. Eight more civilian contractors, such as pilots, also died on deployment with peacekeeping missions in 2012.
Associated Press writers Michelle Faul in Lagos, Nigeria, and Edie Lederer in New York contributed to this report.
Jon Gambrell can be reached at www.twitter.com/jongambrellAP .