Activists have called for the international community to intervene in Sudan after a US group released satellite photos of what appear to be mass graves.

The Satellite Sentinel Project images seems to show freshly dug sites in South Kordofan state, where Sudan's Arab military has targeted an ethnic minority loyal to the military of the newly-formed Republic of South Sudan.

A witness told the project, co-founded by actor George Clooney, that he saw 100 bodies or more put into one of the pits.

"The satellite images contain many details and hallmarks of the mass atrocities described by at least five eyewitnesses to the alleged killings," said Nathaniel A. Raymond, of the Harvard Humanitarian Initiative, which analyses the project's images.

Fighting broke out in the region on June 5. Neither the UN, outside aid groups nor journalists have access to the region, raising fears that more violence is being carried out than is known publicly.

Samuel Totten, a genocide scholar at the University of Arkansas, said: "It is imperative member nations of the United Nations act now in a timely, efficient and effective manner to enter South Kordofan in order to ward off any more mass killings".

A spokesman for Sudan's ruling party denied the project's allegations and said the area is open to observers, though aid groups say it is not.

"Even if there is any suspicion on such pictures, people can go there and visit the area and see the reality," said Rabie A. Atti, National Congress Party spokesman.