Sudan's army has claimed to have killed more than 50 rebels in clashes in Southern Kordofan state, the official Sudanese news agency, SUNA, reported.

Government troops had pushed back an attack by rebels in the region, killing more than 50 and suffering some dead and wounded themselves, SUNA reported late on Friday, citing an army statement.

The clashes took place about 15km from the state capital Kadugli, the army said, blaming the attack on fighters of the Revolutionary Front, an alliance of four rebel groups.

The groups that make up the Revolutionary Front are active in Southern Kordofan, in Blue Nile state to the east and in Darfur to the west.

The conflict in Southern Kordofan and the neighbouring Blue Nile state has had a devastating effect on local people, a top United Nations official told the UN Security Council on Tuesday.

Hundreds of thousands of people there are surviving on roots and leaves, John Ging, UN humanitarian operations director, said. Both Sudan's government and the rebels are blocking access to international aid workers, he added.

Southern Kordofan and Blue Nile border South Sudan, which separated from Sudan in July 2011 under a peace agreement that ended the 1983-2005 civil war.

Khartoum accuses South Sudan of supporting rebels operating in Sudan, including the 19-month rebellion in oil-producing Southern Kordofan. The South, in turn, has said Sudan backs insurgents on its territory.

The issue has been a major obstacle to implementing agreements between the two countries. Key unresolved issues between the two countries include the demarcation of border zones that cut through oil-rich regions.