A priest, a student priest and three nuns, are said to be among those killed on Monday at the town of Kasika 80km from Bukavu in South Kivu province.

All of the dead are thought to be Congolese.

The Vatican said the attack was carried out by Tutsi rebels in revenge for the killing of Tutsi soldiers at the nearby town of Mwenga on Sunday.

Pope John Paul II on Wednesday deplored the massacre.

"It is with deep sadness that I learned the news of the massacre on Monday at Kasika parish in the diocese of Uvira.

"I strongly deplore this criminal act," the pontiff said at the end of a general audience at the Vatican.

The rebels attacked because they suspected local people of giving food to a pro-government militia, the Vatican said.

Jane Standley: "The conflict is splintering alliances across the continent"

BBC Rome correspondent, David Willey says dozens of priests and nuns both foreign missionaries and Africans have been killed in recent years in fighting and in civil war in the Great Lakes region of central Africa.

He adds that the missionary activities of the Roman Catholic Church are crucial to economic and social life in this part of Africa.

Foreign intervention criticised

The massacre comes as President Laurent Kabila's government, aided by foreign troops, continues to battle a three-week-old rebellion.

Mandela: Seeking cease-fire

President Nelson Mandela of South Africa has again criticised Zimbabwe for committing troops to the conflict and called for a negotiated cease-fire.

The Zimbabwean military, which along with Angola is supporting President Kabila, earlier gave its first account of the fighting, saying its air force helped destroy a five-kilometre column of rebel tanks and armoured cars in the south west.

A Zimbabwean spokesman said the priority for the moment was to protect the capital, Kinshasa.

John Nagenda, senior advisor to Ugandan President: "We never sent our troops to fight in Congo"

Zimbabwe says Namibian troops are supporting Mr Kabila. But the Namibians say they are only helping him with logistical support and supplies.

Uganda and Rwanda, which are sympathetic to the rebels, also have troops in Congo - though both countries still deny they are fighting actively on the rebel side.

Protests: Congolese oppose foreign intervention

The BBC correspondent the country, Jane Standley, says there is a sense in Kinshasa that the tide on the western front is now turning in the government's favour.

But claims by the government's Angolan allies to have recaptured the eastern city of Kisangani are unsupported by independent sources.

President Kabila is trying to fight back in the east, using tribal militias. But our correspondent says the battle to reach the rebel lines across vast tracts of thick jungle may be the most difficult one.

Mandela: "Concentrating on a cease-fire"

Earlier, rebel leaders said that hundreds of civilians had been killed in bombing raids carried out by Angolan and Zimbabwean aircraft.

The unconfirmed attacks on civilians are said to have taken place throughout Monday at the rebel frontline around 50km south-west of Kinshasa.