The United Nations has suspended food deliveries to the troubled Sudanese Darfur region following outbreaks of rebel violence and retaliation by the government.
Rebel attacks on government forces on Monday in the town of Ghubeish in an area bordering Darfur meant the region was unsafe for the aid convoys, the World Food Programme said last night.
It suspended three convoys of trucks carrying 1.3 billion tonnes of food aid, cutting off assistance to some 260,000 people in Darfur - described by the United Nations as one of the world's worst humanitarian crises.
A new rebel group, the Sudanese National Movement for the Eradication of Marginalisation, said it had killed 150 soldiers and policemen in Monday's attack, a figure disputed by Sudan's official news agency SUNA which said the toll was far smaller.
Two main rebel groups launched a revolt against Khartoum in early 2003, complaining of neglect and accusing the government of arming Arab militias known as Janjaweed to burn and loot non-Arab villages.
The uprising follows years of clashes over scarce resources in the vast arid region. Peace talks held in Nigeria have stalled.
The WFP called on rebels to return 13 recently stolen aid trucks which it fears are being used for military purposes.
"Such misuses of humanitarian assets should cease immediately," said Mr Jan Pronk, the UN's special envoy to the region. "The parties to the conflict have to live up to their commitments, including their responsibility to ensure the safety and well-being of their own people and their unhindered access to humanitarian assistance".