Aid delivery is in jeopardy for an estimated 100,000 people affected by violence in Sudan's Darfur region unless authorities grant better access, the United Nations warned on Thursday.
One humanitarian agency has said the number of displaced people is the largest in recent years in Darfur, where a decade of civil war has been compounded by inter-Arab violence, banditry and tribal fighting.
But the true extent of the problem is unclear because UN workers have had only limited access to the affected area of Jebel Amir, the UN humanitarian agency OCHA said in its weekly bulletin.
Foreign aid workers, diplomats and journalists routinely face restrictions on their movement in Sudan's far west.
The country's top aid official blamed security conditions for the latest restrictions.
"The UN has informed the Sudanese authorities that it will not be able to continue providing food and other relief unless the relevant UN officials in North Darfur are permitted to travel to the area to register those in need of assistance and to carry out a comprehensive assessment," OCHA said.
Restrictions have been imposed even though the UN and its partners have delivered more than 700 tonnes of food and other relief since the unrest began in early January, OCHA said.
In the past month no foreign UN aid workers have been allowed into the affected area, it said, adding: "The restrictions on access are making it difficult to scale up the aid operation."
Suleiman Abdel Rahman, Sudan's Humanitarian Aid Commissioner, said in a statement to AFP that the government has no policy of denying access.
But he said there are tensions in Jebel Amir and "the security authorities in North Darfur want to be satisfied that the movement of the aid workers is secure."
North Darfur has seen a surge in violence over the past few months.
The mass displacement at Jebel Amir occurred after inter-Arab tribal fighting in a gold mining area.
"With tensions remaining high, there are fears that a new round of fighting may lead to yet more displacement," OCHA said, describing the humanitarian situation as dire.
The global aid agency Oxfam on Wednesday said the newly homeless are forced to defecate in the open, which could lead to disease.
With crops burned during the fighting, Oxfam also warned of possible food shortages.
Aid workers also report security problems on the main road leading to El Sireaf town, where most of the displaced have sought refuge.
Bad roads add to the logistical difficulties, OCHA said.
The US administration's senior adviser to Darfur, Dane Smith, warned in December that funding for recovery of the war-ravaged area is in jeopardy unless restrictions on international aid personnel ease.
Separately, rebels in Darfur confirmed on Thursday that they pulled back from the town of Golo, where the region's insurgency began a decade ago.
"I want to confirm that we withdrew from Golo because we wanted to protect the civilians from NCP bombardment," Ibrahim al-Hillu, spokesman for the Sudan Liberation Army's (SLA) Abdel Wahid Nur faction, told AFP.
He was referring to the ruling National Congress Party.
Rebel leader Abdel Wahid Mohammed al-Nur began the insurrection in Darfur on February 26, 2003 with the seizure and brief occupation of Golo in the Jebel Marra region, southeast of Jebel Amir.
His forces announced last December 24 that they had retaken the town, capturing heavy machineguns, mortars, vehicles and other military equipment.
Prolonged rebel control of a population centre in Darfur is unusual.
Before the latest unrest, 1.4 million people were living in camps for people displaced by Darfur's conflict, the UN said.
Sudan's President Omar al-Bashir is wanted by the International Criminal Court for crimes against humanity, genocide and war crimes allegedly committed in Darfur.