Sudan's president has called for a two-week, unilateral cease-fire in Southern Kordofan state, where government forces are accused of committing atrocities against civilians.

President Omar al-Bashir declared the truce on Tuesday ahead of a fact-finding mission by United Nations agencies to assess the humanitarian situation in the region.

Khartoum organized the mission after the U.N. human rights office called for an investigation into possible war crimes in Southern Kordofan.

The U.N. says it has received reports of indiscriminate killings, widespread looting and massive civilian displacement in the state. It blames most of the violence on Sudan's army, police and allied militia.

Sudan has rejected the claims.

Fighting between government forces and the state's ethnic Nuba rebels began escalating in June, about a month before South Sudan split from the north and declared independence.

The Nuba fighters sided with the south during Sudan's 21-year north-south civil war.

The Khartoum government has ordered former southern fighters in the border state to move into South Sudan.

The U.N. mission is set to arrive in Southern Kordofan on Saturday.