(Aid security) is not the sole responsibility of the coalition and the coalition at this stage cannot secure every road in Afghanistan

Coalition spokesman Kenton Keith

"Insecurity remains a major hurdle for the distribution of humanitarian aid," said UN spokesman Eric Falt.

On Wednesday, UN premises in Jalalabad and Mazar-e-Sharif were looted, while on Monday a World Food Programme (WFP) convoy carrying 185 tonnes of food was hijacked on its way to Herat.

Banditry

The trucks bound for Herat were hijacked by "unidentified bandits" and the food distributed to local residents, according to WFP spokesman Khaled Mansour.

The trucks are now believed to be in the Taleban's southern stronghold of Kandahar.

It was revealed on Wednesday that the Jalalabad offices of other agencies had also been robbed, and that radios, vehicles and office equipment were taken.

A spokesman in Islamabad for the US-led coalition against terrorism said on Thursday protection for aid shipments could not yet be guaranteed all over Afghanistan.

"The coalition has assumed responsibility to provide security for the aid," said coalition spokesman Kenton Keith.

"But it is not the sole responsibility of the coalition and the coalition at this stage cannot secure every road in Afghanistan."

Many dangers

The UN's Mr Falt said there were many dangers facing his staff.

Six million people in Afghanistan depend on aid

"Our truck drivers are not armed and they are at the mercy of whoever is armed. In a case like that, there is nothing we can do.

"Of course we do rely at the same time on the local authorities to ensure the protection of humanitarian assistance and the protection of these routes," he said.

Aid agencies have called on the United Nations to create a multinational force to ensure the aid can be distributed safely.

This would not be the same as a peacekeeping force and would operate in areas where there was the greatest need.

Afghanistan has suffered from a three-year-long drought and millions of people depend on aid.

The UN deputy representative for Afghanistan, Francesc Vendrell, said he backed the idea of a multinational force going to Afghanistan but that it should be a coalition of the willing, organised by one country and not by the UN.