A peacekeeper was shot dead Friday in an attack on an African Union-UN base in Sudan's Darfur, the mission said, two days after the government announced it regained control of the area from rebels.
"In the early morning hours of 19 April, one peacekeeper of the African Union-United Nations Mission in Darfur (UNAMID) was shot dead and two others injured in an attack by unidentified assailants on the mission's team site near Muhagiriya," mission spokeswoman Aicha Elbasri said in a statement.
UNAMID did not release the nationality of the victims but Muhagiriya falls under the jurisdiction of Nigerian peacekeepers.
"UNAMID is investigating the events surrounding the incident and working in coordination with (the) government of Sudan to ensure that the perpetrators are brought to justice, as any attack on international peacekeepers is a crime under international law," Elbasri said.
More than 40 peacekeepers have been killed in hostile action during UNAMID's five-year history and the UN has repeatedly called for perpetrators to be brought to justice
However, UN sources have said they were unaware of anybody previously being held accountable in Sudan for killing a peacekeeper.
In February a UN panel of experts reported that former members of government militias "have forcibly expressed their discontent with the current government," including through occasional cases of "direct attacks on UNAMID staff and premises".
Ethnic rebels in Sudan's far-western Darfur region rose up against the Arab-dominated Khartoum government in 2003.
In response, government-backed Janjaweed militia shocked the world with atrocities against ethnic Africans.
While the worst of the violence has long passed, instability has been complicated by inter-Arab fighting, kidnappings, carjackings and other crimes, many suspected to be the work of government-linked militia and paramilitary groups.
A rare 10-day rebel occupation of Muhagiriya and Labado in southern Darfur ended on Wednesday when the Sudanese army announced it "liberated" the area but the insurgents said they withdrew in the face of massive force.
The Sudan Liberation Army's Minni Minnawi faction on April 6 took control of the two communities strategically located about 100 kilometres (60 miles) east of the South Darfur state capital Nyala, one of Sudan's largest cities.
Darfur's insurgents normally stage hit-and-run attacks.
Rebel splinter factions signed a 2011 peace deal with the government but Minnawi and other major insurgent groups rejected the agreement.
The army had already regained control of Labado on Tuesday after fierce fighting which resulted in the deaths of four civilians, UNAMID said.
By early this week an estimated 40,000 people had been displaced by fighting in the area, the UN's Office for the Coordination of Humanitarian Affairs (OCHA) said in its weekly bulletin on Friday.
"Reports from agencies in the area indicate that the entire population of Muhagiriya may have fled the town," it said, adding that most of those who escaped sought shelter around the local UNAMID bases.
It said the government, citing security concerns, has not allowed aid groups to reach the area "despite concerted advocacy from humanitarian organisations".
Local authorities said an aid mission would soon be allowed into the district, OCHA reported.
In other unrest, OCHA said "fierce fighting" continued between the Salamat and Misseriya tribes in Umm Dukhun district near the Chad border, with reports of related unrest in Rahad el Berdi town.
Sudanese Interior Minister Ibrahim Mahmoud Hamed said in statements published Thursday that Darfur is largely calm except for some rebel "looting" and attacks on commercial convoys.
But Vice President Ali Osman Taha last Sunday warned over insecurity in South Darfur, and Canada said at a conference last week in Qatar that security in Darfur has "worsened".