Kenya's main opposition parties have teamed up with dissidents from the ruling party and are aiming to field a single candidate in presidential elections due in December.

Plans were announced to form an alliance, called the Rainbow Coalition, at a large rally in the centre of Nairobi.

Presidential candidates

Kanu - Uhuru Kenyatta Rainbow Coalition - To be decided NAK - Mwai Kibaki

Earlier on Monday, the ruling party in Kenya, Kanu, endorsed Uhuru Kenyatta, as its official candidate for the elections.

The 41 year old - the son of Kenya's first president, Jomo Kenyatta - has the backing of the current President, Daniel arap Moi, who is due to retire after 24 years in power.

Many senior Kanu party figures opposed President Moi's choice, and six government ministers resigned in the past two days.

Opposition unites?

The dissidents, who call themselves the Rainbow Alliance, boycotted the nomination meeting and announced their own party - the Liberal Democratic Party which they said was teaming up with the second biggest opposition grouping, the Ford People party.

Leading Rainbow Alliance member and former energy minister, Raila Odinga, said they were now in negotiations with the main opposition grouping, NAK, seeking to come up with one candidate to oppose Uhuru.

Uhuru Kenyatta: President Moi's man

"The Rainbow Coalition will proceed with talks with all democratic forces to form a coalition to bring the change that Kenyans desire," he said.

In a surprise move, Charity Ngilu, a leading member of NAK, appeared at the rally saying: "All of us would have wanted to rule this country, but you know Kenyans want us to unite."

"There is no turning back," she said.

Manipulation?

Earlier, Mr Odinga denounced the Kanu gathering as a farce and said no-one could expect fair play.

Around 50,000 people attended the opposition rally

The dissident group accused President Moi of forcing Kanu delegates to accept his preferred choice of successor, instead of allowing the nomination to happen through a democratic process.

They also accuse him of choosing Mr Kenyatta as his successor so that he can manipulate him from retirement.

Mr Moi has said the businessman, who only recently became a minister, is a "young man who can be guided".

Accepting the nomination, Mr Kenyatta praised President Moi and said if elected he would seek his advice on running the country.

Opposition alliance

If the opposition can agree a single candidate they would have their best chance in 40 years to remove Kanu from power.

Kibaki is running again

However, in the past two elections the opposition have sought to unite, failed and been defeated by President Moi.

And NAK has already nominated veteran opposition leader Mwai Kibaki as their candidate.

Mr Kibaki and Mr Kenyatta are both Kikuyus, Kenya's largest ethnic group.

Our correspondent in East Africa says Kanu remains the most powerful and well-organized party in Kenya and wth the power of the state behind him, Uhuru will be a formidable candidate.

Kenyans, used to President Moi's authority, have been riveted by the furore caused by his support for Mr Kenyatta and by the sight of his previously loyal ministers turning against him and splitting the ruling party.