The Kalenjin gangs arrived just after midnight. Witnesses said that hundreds of youths went from shack to shack singling out homes belonging to members of the Kikuyu tribe, setting light to each one as sleepy families stumbled to safety.

By the morning 30 homes had been razed in the small town of Londiani, bringing the total to more than 1,000 in three weeks of violence since Kenya’s disputed elections.

Residents throughout the Western Rift Valley say that the violence is no longer about the election. They say it is a form of ethnic cleansing as the Kalenjin seek to reclaim their ancestral lands from members of ethnic groups from other parts of Kenya.

Macharia Isaac, 34, a Kikuyu, fled his home on Sunday night for the safety of St Kizito’s Church. “We left because we know it’s going to get much worse,” he said. “This last time the Kikuyus decided to burn Kalenjin houses in retaliation. It has just gone too far.”

International observers say that a flawed tallying process makes it impossible to confirm that President Kibaki won most votes in the December 27 poll. Since then his supporters from the Kikuyu tribe have been targeted by opposition gangs in violence that has killed about 650 people and displaced 250,000.

Raila Odinga, the main opposition leader, says that the only solution is a rerun of the election. He is backed by Kalenjin and other ethnic groups opposed to the Kikuyu.

Peace returned to much of the country after a wave of bloodletting following the elections when opposition demonstrations ended last Friday. The Western Rift Valley is a bloody exception. Father Brian Treacy, one of three Irish priests at St Kizito’s, said that the violence was directed at opposition supporters and Kikuyu in equal measure. “This is about ethnic cleansing, nothing else,” he said.

About 3,000 people have gathered in the yard around his church since the attack on Sunday night. Father Treacy said that people arriving believed the violence had been orchestrated. “It’s like a military operation,” he said. “They come from ten different corners at the same time, armed and with fuel to start fires.”

The intimidation is working. A steady stream of cattle lorries loaded with people, mattresses and furniture is leaving Londiani. The United Nations estimates that 1,000 people are arriving each day in Nakuru, which has become a hub for aid agencies. Most are Kikuyus trying to reach safety. Those in Londiani also include Kalenjins whose businesses were destroyed in the first signs of retaliation. “Raila and Kibaki must agree,” said Joel Chelule Kaptich as he picked through the ashes of his butcher’s shop, workshop and small hotel. “Until then there will be no improvement.”

President Museveni of Uganda met Mr Kibaki yesterday in an attempt to defuse the crisis.

Kofi Annan, the former UN Secretary-General, arrived in the Kenyan capital Nairobi last night as part of the latest mediation effort. He faces an uphill struggle to find common ground. Both sides appeared to have strengthened their positions in recent days with newspaper adverts setting out their grievances.

The Government, in particular, has tackled international criticism head on, calling in Adam Wood, the British High Commissioner, to explain why London was refusing to recognise Mr Kibaki as President. It has also tried to accuse the international community of stirring up violence by questioning the election results.

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