NAIROBI - Kenyan President Mwai Kibaki will meet his rival Raila Odinga on Thursday for the first time since a disputed election fuelled weeks of riots and ethnic violence, the United Nations said.

The meeting would be a major breakthrough in the bloody crisis. Despite strong international pressure and to the frustration of millions of Kenyans, the two leaders have failed to talk since the December 27 vote.

News of the meeting came after former U.N. Secretary-General Kofi Annan met Kibaki at State House in the latest bid to end unrest that has killed nearly 700 people.

"At 4.30 p.m (1:30 p.m. British time) today there will be a meeting between Kofi Annan and President Kibaki and Honourable Odinga at (the) office of (the) president, Harambee House," a U.N. spokesman said in a statement to media.

Word of the meeting came as a human rights watchdog accused opposition party officials of organising tribal violence in the country's Rift Valley, echoing government allegations.

Odinga and other officials from his opposition Orange Democratic Movement (ODM) met Annan late on Wednesday, and at his request agreed to call off protests planned for Thursday over a victory it says Kibaki stole.

The opposition demanded an outside mediator to solve a crisis that has split Kenya down tribal and political lines, after Kibaki narrowly won the closest election in the east African nation's history in a vote rife with rigging.

Hundreds have died and 250,000 been forced to flee their homes in a combination of ethnic killings fuelled by politics and police action - criticised as excessive - during earlier protests that degenerated into rioting and looting.

In Odinga's stronghold of Kisumu in western Kenya, several youths burned tyres, saying they were angry he had been caught in police teargas on Wednesday at a memorial service.

ETHNIC KILLINGS

On Thursday, Human Rights Watch (HRW) said it had "evidence that ODM politicians and local leaders actively fomented some post-election violence", in the Rift Valley.

"Opposition leaders are right to challenge Kenya's rigged presidential poll, but they can't use it as an excuse for targeting ethnic groups," HRW's Georgette Gagnon said.

The Rift has seen some of the worst violence in the crisis, including the burning of 30 members of Kibaki's Kikuyu ethnic group in a church by members of the Kalenjin tribe.

HRW said at least 400 had been killed in ethnic clashes there, and that ODM mobilisers and local elders urged Kalenjins "to contribute money toward the purchase of automatic weapons".

It quoted Kalenjin sources who said plans were still in place to attack camps of displaced Kikuyus and thus-far intact Kikuyu areas. It urged police to step up protection.

The violence has shattered Kenya's image as a stable, democratic country with the region's strongest economy. Its core tourism industry has seen mass cancellations and its shilling currency hit an 18-month low on Wednesday.

ODM said it has no faith in Kenya's courts and especially the Electoral Commission of Kenya (ECK), internationally criticised for its handling of the vote counting.

The ECK's December 30 announcement that Kibaki won amid claims of rigging on both sides inflamed parts of the country already tense or breaking out in violence over the delayed tallying.

The ECK in a newspaper advertisement on Thursday shot back at accusers, saying media had incorrectly quoted Chairman Samuel Kivuitu as saying "I don't know" when asked if Kibaki won.

"The actual question posed ... was 'do you believe that Mwai Kibaki fairly won the election? ... the media has deliberately distorted this question to remove the word fairly to create the impression that ECK is uncertain as to who won," the ad says.