A U.S.-based group says new satellite imagery has identified three new mass graves in the southern part of Sudan.

The Satellite Sentinel Project released images Wednesday of what it says are two piles of corpses wrapped in body bags or tarps on a mountainside in Kadugli, in Sudan's Southern Kordofan state.

The satellite monitoring group says other images and eyewitness accounts indicate that pro-government forces are trying to cover up a third mass grave beneath a water tank in the same city.

During June, forces allied to what were then northern and southern Sudan clashed in the state.

On Monday, the United Nations human rights office called for an investigation of alleged war crimes committed in Sudan's Southern Kordofan state. The office said it has received reports of indiscriminate killings, widespread looting and massive civilian displacement in the state.

The fighting preceded South Sudan's split from the north in July, six years after a long civil war.

The U.N. report blames most of the abuses in Southern Kordofan on the north's army, police and allied militia.