Rwanda, one of the main supporters of the rebel forces, said it had not been consulted about the agreement, which it described as null and void.

The rebels themselves have vowed to continue their fight against Congolese President Laurent Kabila.

"It will not have an immediate effect on the ground. We will continue fighting," said rebel leader Ernest Wamba dia Wamba.

Earlier, Uganda, which attended the talks in Libya, said it had no plans to withdraw its troops until its border with Congo was secure.

Uganda is backing the Congolese rebels, who have seized about a third of Congolese territory from Mr Kabila's government.

The agreement signed by President Kabila and other African heads of state in the Libyan town of Sirte called for a ceasefire, a withdrawal of all foreign troops and the deployment of an African peacekeeping force.

No rebel representatives were present at the signing.

On Tuesday Jean-Pierra Bemba, leader of the Congolese Liberation Movement (MLC), the smaller of the two main Congolese rebel movements said he was "not involved" in the ceasefire agreement and vowed to continue fighting.

'Prelude to peace'

President Laurent Kabila: "The invaders will never leave unless they are forced"

President Kabila had earlier described the accord as a "prelude to peace", but said his countrymen must continue to prepare for war against the rebels.

"The invaders will never leave unless they are forced" Mr Kabila told Conglese state television.

"We cannot claim to make peace when an entire half of the country is occupied by the invaders," the president added.

But he insisted that President Museveni had promised to withdraw the Ugandan troops who are fighting alongside the rebels.

"When one makes such a pact one has to respect it," Mr Kabila said.

Rebels expected at talks

The Congolese Information Minister, Didier Mumengi, said both Dr Wamba and Mr Bemba had agreed to take part in peace talks in Rome at the end of April.

However, both rebel leaders told the BBC that certain conditions had to be met before the talks.

Dr Wamba said the government delegation consisted of what he called "dinosaurs-in-exile", trying to secure their return to Kinshasa.

Mr Bemba said political prisoners had to be released and political parties allowed to operate freely.

Observer troops

Mr Kabila said on Monday that Libya and Eritrea had agreed to send observer troops to replace Ugandan forces he accuses of invading parts of Congo.

However, he postponed publicly announcing the anxiously-awaited details of the accord.

The war, which has pitted the Kabila government against Tutsi-led rebels backed by Rwanda, Uganda and Burundi, has wreaked havoc on the population and the fragile economies in the region.