NAIROBI, KENYA, OCT. 27 -- The Ethiopian rebel group that last Friday ambushed and burned a convoy of U.N. trucks carrying emergency food today threatened to attack other famine-relief convoys in the drought-stricken north of that country.

A spokesman for the Eritrean People's Liberation Front (EPLF) said that unless the rebels are informed in advance about the movement of U.N. convoys, they will assume the trucks are being used as "camouflage" for military activities of the Ethiopian government.

"It is not the wish of the EPLF to deter relief activities, but if we are not informed of what is going to happen, we don't have any choice," said Tesfaye Ghermuzian, spokesman in Washington for the rebel group. "We cannot be blamed for any consequences and casualties that might happen."

In the Ethiopian capital of Addis Ababa, a senior U.N. official replied that "it is out of the question" for the U.N. emergency operation to establish contacts with the Eritrean rebels.

"In Ethiopia, we don't have any contact with any organization other than the government and we certainly cannot start such contact," said David Morton, director in Ethiopia of the U.N. World Food Program.

Rebels in Eritrea have been fighting for independence from the Addis Ababa government for nearly 27 years. It is the world's longest continuous civil war.

The face-off between the Eritrean rebels and the United Nations comes as western donors try to rush supplies of relief food into the northern Ethiopian regions of Tigray and Eritrea, where severe drought threatens at least 1 million people with starvation.

If large amounts of food do not reach the north by December, donors warn that large numbers of destitute people will migrate into famine shelters. It was in such shelters in 1984-85 that hundreds of thousands of people died.

The rebel attack last Friday -- in which rebels destroyed 23 long-haul trucks valued at more than $2 million, along with 450 tons of wheat that could have fed 45,000 people for a month -- was an unexpected and severe setback for relief officials trying to organize timely delivery of food.

"We have lost a lot because of this," said Morton. "We have lost time. We have lost food. We have lost trucking capacity. And there is now uncertainty about whether any trucks can move freely in that part of the country."

Lack of transport is the major obstacle to moving the 400,000 tons of food aid that donors say is needed to stave off famine in northern Ethiopia next year. Friday's attack destroyed about 40 percent of the United Nations' long-haul vehicles in Eritrea and Tigray.

The U.S. Agency for International Development (AID) had been considering buying new trucks for northern Ethiopia, where a recent donor report found that 300 additional long-haul vehicles are urgently needed.

The rebel attack, however, has "put everything on the back burner," according to Rick Machmer, AID director in Ethiopia.

Donors acknowledge that they have little time to ponder their options if they want to prevent the famine-camp conditions that caused large numbers of deaths in the 1984-85 famine. In Tigray, destitute farmers and their families reportedly have already begun to leave their farms and walk toward cities looking for food.

"If the food pipeline dries up, or if the number of destitute people increases in the next few weeks, we will be back in a shelter situation," said Morton. "It is very critical."

In a telephone interview today, EPLF spokesman Tesfaye said it is "very unfortunate that the trucks carrying the food were burned." But he insisted that the attack was "not a mistake" and that three of the trucks in the convoy were carrying "bullets and bombs" belonging to the Ethiopian government.

"The government is known to us to carry military personnel and hardware by camouflaging them in food convoys. This area {in Eritrea where the attack occurred} is in a combat zone. There was no time to distinguish between which trucks were carrying food and which ones were not carrying food."

American and U.N. officials in Addis Ababa today categorically denied that there were any military vehicles or any hidden arms in any of the convoy's 23 trucks. Sixteen of the trucks flew the flag of the United Nations; the others belonged to the Catholic Secretariat of Ethiopia.