NEW FANJAK, southern Sudan, May 18, 2005 -- Part of a major UN aid operation in Sudan has been suspended and is under review after a militia leader blocked the delivery of food.

A barge convoy down a tributary of the Nile had been delivering food to both government and former rebel areas in the south of the country.

It had, until now, been considered a successful confidence-building mission.

Militias loyal to the government are said to be one of the biggest threats to peace in southern Sudan.

Under the peace agreement, they are supposed to disband themselves.

'Too dangerous'

The UN was supposed to deliver the food aid to a hungry local community.

The delivery was stopped when a local pro-government militia leader demanded that the quantity of rations be doubled.

When the UN rejected his request, he insisted the 150 tons of grain be taken away, depriving the 6,000 people of New Fanjak, as well all those in other villages down this tributary of the Nile.

With the militia upset, it has been deemed too dangerous to continue.

"This is a major setback to the operation now, and this has to be solved," says Hans Wikoler of the UN's World Food programme in charge of the mission.

A security team will arrive soon to assess whether other tributaries are now safe for distribution.

The UN had hoped to reach 150,000 people in remote locations.

Militia threat

Militia violence in southern Sudan, and in particular this area, Upper Nile, is one of the biggest threats to this country's much trumpeted peace agreement.

Originally armed and supported by the Khartoum government to fight the rebels, they have found themselves without a role and frozen out of negotiations.

The peace deal calls for them to disband and join either the army of the government or former rebels.