"We are appealing to authorities in Kadugli, capital of the state of South Kordofan in Sudan, as well as to the central government in Khartoum to allow air and road access for humanitarian agencies," said Melissa Fleming, spokeswoman for the UN High Commissioner for Refugees.
Heavy fighting between forces from the north, including both the Sudanese Armed Forces northern army - or SAF - and government-back forces, and fighters aligned to the Sudan People's Liberation Army (SPLA), the former southern rebel group - has raged across South Kordofan since June 5.
Fleming noted that aid planes have been denied authorisation to land and roadblocks were hampering access by land. "Our operations are severely restrained. We are unable to reach our warehouses which are five kilometres (three miles) away," she said.
Meanwhile the World Health Organisation said medical supplies and office equipment had been stolen from its offices, warehouses and guesthouse in Kadugli last Friday.
The World Food Programme also said its premises had been looted and the agency lost two vehicles and one motorcycle.
But its warehouse in Kadugli was "reportedly being guarded by local authorities and is reportedly undamaged," said Emilia Casella, spokeswoman for the UN food agency.
"However, we're restricted from having access to it. At the moment, our food stocks in other locations are being used but the warehouse in Kadugli we don't have access to," she added.
Fighting in Southern Kordofan has raised tensions at a sensitive moment for Sudan, with the south set to declare independence in less than a month.