The death toll has climbed to nearly 100 people in the latest bout of ethnic violence in Kenya's Rift Valley as mediators struggle to end the month-long crisis.

In Nakuru, a mortuary worker said 64 bodies were lying in the morgue, all victims of the past four days of ethnic fighting.

In nearby Naivasha, a witness reported seeing 32 bodies in the morgue.

Groups from rival communities have been fighting each other with machetes, clubs, and bows and arrows in both towns, famous for their lakes teeming with wildlife.

In the worst incident of the latest flare-up, 19 people were burned to death locked inside a house in Naivasha on Sunday, police officer Grace Kakai said.

The nationwide death toll is now more than 800.

The tit-for-tat violence has complicated the job of former UN chief Kofi Annan, who has asked both sides to name teams to negotiate an end to the electoral crisis that has laid bare the tribal undercurrents of Kenya's politics.

The violence since Kenya's December 27 election has taken on a momentum of its own, with cycles of killing and revenge between tribes.

Britain's Africa minister Mark Malloch Brown said on a visit to Kenya: "What is alarming about the last few days is that there are evidently hidden hands organising it now. Militias are appearing ... the targeting is very specific."

The government has for weeks accused the opposition of organising ethnic killings in the Rift and last week watchdog Human Rights Watch made the same accusation after having said police used excessive force in crushing opposition protests.

The opposition has said that police and criminal groups - in particular the outlawed Mungiki gang - have been dispatched against their supporters.

The dispute over President Mwai Kibaki's re-election - which the opposition says was rigged - has plunged Kenya into a spiral of violence, battering its image as an east African trade and tourism hub and one of the continent's more stable nations.

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