United Nations international staff have returned to Sudan's South Kordofan for the first time in months, the UN said on Saturday, as global concern mounts over food shortages in the war-torn state.

"Today, FAO and OCHA flew back there by helicopter and they landed safely" in the state capital of Kadugli, Damian Rance, a public information officer at the UN Office for the Coordination of Humanitarian Affairs (OCHA), told AFP.  FAO is the UN's Food and Agriculture Organisation.

Sudan severely restricts the work of foreign relief agencies in the state where fighting broke out last June. For months, expatriate aid workers had not been allowed into South Kordofan or Blue Nile, where a similar conflict began in September.

The first expatriate staff to return, from the UN children's agency and the UN security bureau, arrived in Kadugli on Friday by road, Rance said. "This follows a decision made earlier by the government of Sudan to authorise their return," Mark Cutts, who heads OCHA's office in the country, said in a statement.

The international staff who went back are office heads, so their arrival "essentially boosts the skill sets" available to assess people's needs and coordinate aid distribution if foreign relief workers are granted wider access to the region, Rance said.

UN officials have repeatedly said they need full access – including to rebel-held areas – to properly assess the needs of the people.

The US special envoy for Sudan, Princeton Lyman, said last month that the food situation is so dire that Washington warned Khartoum it would consider ways for aid to be sent in without Sudanese government approval.

On Thursday, Sudan's Humanitarian Aid Commission presented the results of an assessment which showed the food situation in 11 of 19 South Kordofan districts was good. It did not mention the other eight districts.

After conducting its own assessment, the UN's World Food Programme gave food last week to about 17,000 needy people who had fled to the outskirts of government-held Kadugli after recent fighting elsewhere in South Kordofan.

Ethnic minority insurgents from the Sudan People's Liberation Movement-North, who fought alongside the former rebels now ruling South Sudan, are battling government troops in South Kordofan and Blue Nile.

South Sudan became independent in July last year after an overwhelming vote for secession that followed more than two decades of civil war.

"We believe that unless we're able to mount a humanitarian operation that has the consent of all sides, the situation there is going to deteriorate very rapidly," Cutts told AFP earlier. He said aid agencies "are waiting for a positive response from the government" on a joint proposal by the UN, African Union and Arab League to assess the needs and deliver aid throughout the conflict area.