An ambush in Sudan's western Darfur region killed four peacekeepers and wounded eight, the UN-African Union Mission (UNAMID) said on on Wednesday.
The attackers struck yesterday in the West Darfur state capital El-Geneina, the peacekeeping force said.
"The incident, which involved a Nigerian military patrol, occurred approximately two kilometres (just over a mile) from the mission's regional headquarters," the force said.
"UNAMID personnel, who were heavily fired upon from several directions, returned fire. UNAMID and local authorities are working at the scene of the incident."
UNAMID Force Commander Lieutenant General Patrick Nyamvumba called on the Khartoum authorities to hunt down those responsible.
"The mission condemns in the strongest terms this criminal attack on our peacekeepers who are here in the service of Darfur's people. I call on the government of Sudan to bring the perpetrators to justice," he said.
Ethnic minority rebels rose against the Arab-dominated Khartoum government in 2003. In response, the government unleashed state-backed Janjaweed Arab militia in a conflict that shocked the world and led to allegations of genocide.
The UN estimates at least 300,000 people died but the government puts the toll at 10,000.
UNAMID has been in Darfur for more than four years with a mandate to protect civilians in the vast area the size of France.
Although violence is down on its peak, clashes between rebels and government troops, banditry and inter-ethnic fighting continues.
Key rebel groups refused to sign a deal reached last year between the Khartoum regime and an alliance of smaller rebel splinter factions.
With more than 22,000 international troops and police officers, UNAMID has a budget of about USD 1.4 billion for 2012-13.