Rebel forces in the Democratic Republic of Congo say they're not deterred by the announcement of a new offensive against them in the east of the country involving troops from Zimbabwe, Angola and Namibia.

The three countries, allies of President Laurent Kabila, have said their forces will strike at rebel strongholds.

A spokesman for the rebels Arthur Z'ahidi Ngoma said Zimbabwe was already involved in fighting in the east, and his troops were holding sixteen Zimbabwean prisoners-of-war as proof.

He said Zimbabwe, Angola and Namibia had become involved in what he called an indefensible cause, and urged them to withdraw.

Earlier, the Zimbabwean President, Robert Mugabe, said the alliance was ready for a prolonged war and promised victory.