Senior army officer Brigadier Joo Jota Manuel said the army has been told by Unita prisoners that the UN staff were in good condition, and being held in the Unita-controlled areas of Bailundo and Andulo - near the crash site

He said that he did not know how many of the 14 passengers and crew had survived. So far, there has been no comment from Unita.

A spokesman for the UN Mission in Angola, Hamadon Toure, confirmed the report is being investigated.

Earlier, officials said the Angolan Government had given security guarantees to allow a UN team to travel to Huambo - 500km south-east of the capital, Luanda - where the cargo plane went down last week.

The UN mission is reported to be seeking similar guarantees of safety from Unita.

Artillery barrage

The UN blames Unita leader Jonas Savimbi for the renewed violence

The aircraft crashed in an area where government forces and Unita rebel troops have been fighting for weeks. It was reported to have been shot down minutes after taking off from Huambo airport.

The UN evacuated staff from Huambo after a major rebel artillery barrage on Wednesday. The shelling reportedly killed at least six people and wounded around 20.

Huambo, Angola's second-largest city, is held by the government and is used by the army to fly in reinforcements for fighting in surrounding areas.

In its latest report on the fighting in the central highlands, the Angolan government says its troops have gained control of the town of Chilonda from Unita forces. Angolan radio said Unita had suffered heavy casualties.

UN deadline

The UN says it had asked several times for a ceasefire in the area around the crash, but until now both the government and Unita had denied receiving any request.

A resolution had set a deadline of 11 January for co-operation by Angolan forces, making a threat of further action, but stopping short of explicitly mentioning military intervention.

Angola's Defence Minister Pedro Sebastiao said on Thursday the government would ''co-operate in every way possible''.

"We are available to create the conditions so that the United Nations can carry out their duty, but this does not only depend on us," he added.

The UN has blamed Unita for the return to war. It says the rebels have refused to yield areas under their control and maintained a hidden army.