United Nations: Sudan has agreed to let UN relief agencies into its troubled South Kordofan state where government troops are battling rebels, UN officials said.

There have been growing international demands for access to the state after a UN report last week said there had been extrajudicial killings and widespread disappearances in South Kordofan.

Tens of thousands are believed to have fled their homes since June and a US envoy said recently the Sudanese government had threatened to shoot down UN flights that went there.

A four-day assessment of food and relief supplies in South Kordofan will start on Sunday in the main city of Kadugli, UN deputy spokesman Farhan Haq said on Friday.

The mission will be led by the Sudanese government's humanitarian aid commissioner and "several" UN agencies," Haq added. "The mission hopes to carry out assessments in several locations."

Sudan's UN ambassador, Daffa-Alla Elhag Ali Osman, said six UN agencies would be involved in the trip.

Susan Rice, the US ambassador to the United Nations, said on Tuesday there was an "increasingly dire" situation in South Kordofan, where government forces have been fighting rebels close to rival South Sudan.

A report by the UN High Commissioner for Human Rights and the UN mission in Sudan, released Monday, detailed "extrajudicial killings, arbitrary arrests and illegal detention, enforced disappearances and attacks against civilians" in South Kordofan in June.

It also described the aerial bombardment of civilian areas in Kadugli.

The UN said the allegations could amount to crimes against humanity or war crimes. The Sudan government labeled the report as biased.

Russia and China have blocked US attempts to get the UN Security Council to condemn the Sudanese bombing and other military activities, diplomats said.