Angola's Unita rebel movement said yesterday that it would co-operate with the United Nations in its search for two crashed UN planes after meeting the world body's representative in the country.

''Issa Diallo called us. He spoke with our general secretary and the contacts have been established to cooperate with the search for the two planes shot down,'' Unita foreign affairs spokesman Alcides Sakala said.

The Angolan government, which on Wednesday pledged its full support in a search for the planes, and Unita have in turn accused each other of shooting down the two transport aircraft.

Unita has until now maintained that it has yet to receive a formal UN request for assistance in finding the aircraft.

The rebel grouping said in a statement that its leader Jonas Savimbi had sent a letter to the US State Department in which he said he shared international concern about the Angolan situation, and especially the downing of the two planes.

Savimbi also responded to a US request in saying that Unita was ready to co-operate with the UN in this context of concern.

The first UN-leased Hercules crashed on December 26 with 14 passengers and crew aboard. The second UN plane was shot down on Saturday with five passengers and four crew.

Both crashed in rebel-held territory. Unita has denied shooting down the aircraft, but has repeatedly said that there are no survivors.

Diallo, head of the UN observer mission in Angola, has so far failed to obtain a ceasefire between the Angolan government and Unita to allow a full search for possible survivors.

Fighting continued yesterday with reports of renewed Unita shelling of the besieged highland town of Malanje, where the death toll has exceeded 50 this week.

The attacks came as Australian diamond mining company Ashton Mining said four of its employees - Briton Patrick Bergin, Brazilian Mario Trepechio, and two Angolan security guards - were killed in an attack on the Cuango mine on Wednesday.

''They were killed in an ambush on their vehicle by an armed band believed to be Unita rebels,'' Ashton said in a statement.

The Vatican said yesterday that three Roman Catholic clerics had been murdered in central Angola. It said that Father Albino Saluhaku and two of his aides had been ''barbarically killed''. It gave no further details.

The downing of the planes prompted the United Nations to suspend flights around Angola and reconsider its position in the oil and diamond-rich southern African country.

The UN mission was set up to monitor the implementation of the 1994 peace accord, which is effectively in tatters after the civil war that plagued Angola since independence from Portugal in 1975 re-erupted in earnest.-Reuters