Peter Greste reports on the latest developments in Congo

Joao de Matos appeared before the press in the strategically important Congolese port of Matadi which his troops gained control of at the weekend.

The strategic port of Matadi is back into government control

He said Angola had intervened on the side of the Congolese President, Laurent Kabila, "to protect the legal government of the Democratic Republic of Congo" and "to protect the vital interests of Angola".

Mr de Matos said his troops controlled the whole of south-western Congo.

Angola is understood to be concerned that if the Congolese rebels win power, they may give aid to the rebel Unita movement in Angola.

Unita members arrested

Jorge Chikoti: "Now we have true evidence that there has been... co-operation [between Unita and the Congolese rebels]"

In a separate development, Angola says its military forces have captured members of the Angolan rebel movement, Unita, inside the Democratic Republic of Congo.

The Angolan Deputy Foreign Minister, Jorge Chikoti, told the BBC that Angola had "true evidence" that Unita was supporting Congolese rebels against President Kabila.

Mr Chikoti also said there had been "an unprovoked invasion" of Congo by Uganda and Rwanda.

Jorge Chikoti: "We think that under no pretext possible should a country invade the other country"

"This violates a principle of sovereignty and territorial integrity," he said.

Mr Chikoti said Angola's intervention followed President Kabila's appeal to the southern African grouping, SADICC, earlier in August.

Angola's crucial role

Mark Doyle: "The role of Angola is critical"

The BBC West Africa correspondent, Mark Doyle, says the role of Angola is critical as its civil war might spread and various alliances in the area may be at stake. It has one of the largest armies in Africa.

Two other African countries - Zimbabwe and Namibia - have also sent troops into Congo to help the government of President Laurent Kabila defeat the one-month-old rebellion.

Rwanda and Uganda have denied allegations that their forces have intervened on the side of the rebels.

Kabila vows to counter-attack

President Kabila thanked Zimbabwe for its support

President Kabila said on Sunday, during a visit to Zimbabwe, that the Congolese and the allied troops "are preparing a counter-offensive" against the rebels.

But the leader of the rebels, Jean-Pierre Ondekane, said the fight to overthrow him would continue.

The governor of the capital, Kinshasa, has thanked the local population for helping to flush out rebels who had appeared in the suburbs of the city.

In a radio broadcast on Monday, he asked civilians to hand over alive any captured rebels or any rebel weaponry to the authorities.