(CNN)  -- Seven members of a joint United Nations-African Union peacekeeping patrol have been killed by a heavily armed militia group in Sudan's Darfur region, the U.N. said. Peacekeepers drive into a Sudanese refugee camp near Farchana, east of Chad. Five of those killed were Rwandan, a U.N. peacekeeping official said, and the other two were a Ugandan and a Ghanaian. Twenty-two others were wounded in the attack, which was immediately condemned by U.N. Secretary-General Ban Ki-moon. "The attackers used heavy weapons and engaged the UNAMID convoy in an exchange of fire for more than two hours," according to the statement released by Ban's spokesman.

"The secretary-general condemns in the strongest possible terms this unacceptable act of extreme violence against AU-
U.N. peacekeepers in Darfur and calls on the government of Sudan to do its utmost to ensure that the perpetrators are swiftly identified and brought to justice," the statement said.