An attack which killed a peacekeeper in Sudan's Darfur region last week appears to have been planned and carried out by government-linked forces, local sources in the area told AFP on Monday.
One Nigerian Blue Helmet was killed and two other peacekeepers were wounded in Friday's assault against a base of the African Union-UN Mission (UNAMID) near Muhagiriya town in southern Darfur.
Two days earlier the Sudanese army announced it had regained control of the area from rebels.
The attack "looks like it was planned and conducted by forces aligned with the government," one source said, asking for anonymity.
Local sources said peacekeepers returned fire, killing at least one of the attackers.
Sudan's army spokesman could not be reached for comment.
On Sunday the US charge d'affaires to Sudan, Joseph Stafford, condemned the attack on the peacekeepers. He told reporters it is not yet clear who carried out the "deeply troubling" assault but said security in Darfur is worsening and militias need to be disarmed.
"We're worried about the deteriorating security situation in Darfur and the conflict between the government forces and the militia", Stafford said.
In February a UN panel of experts reported "some incidents in which former members of government militias have forcibly expressed their discontent with the current government, especially against the backdrop of rising inflation and unemployment."
It said this discontent has occasionally led to "direct attacks on UNAMID staff and premises".
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.
Rebels have been fighting for 10 years in Sudan's far-west Darfur.
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.