NAIROBI (Reuters) - President Mwai Kibaki's government accused political rival Raila Odinga on Wednesday of total responsibility for an explosion of tribal violence over a disputed presidential poll that threatens to tear Kenya apart.

"It has been one-way all the way. It is basically Raila Odinga-led ethnic cleansing of the Kikuyu (tribe),," government spokesman Alfred Matua told the BBC as the death toll from four days of clashes in the East African country neared 250.

Supporters of Odinga, who comes from the Luo tribe, have in turn made ethnic cleansing charges against Kibaki, whose Kikuyu tribe has long dominated political and business life in Kenya, East Africa's biggest economy.

Young men armed with machetes manned roadblocks on Wednesday, hours after about 30 Kikuyus were burned alive when a mob set fire to a church where they were hiding near the western town of Eldoret.

Adding to the chaos, the head of Kenya's electoral commission, Samuel Kivuitu, was quoted as saying he did not know whether Kibaki had won the presidential poll.

The statement attributed to Kivuitu, who announced on Sunday Kibaki had narrowly won, could not be immediately verified.

Western powers have called for calm and warned citizens against visiting a popular tourist destination that was regarded as one of the most stable democracies on a volatile continent.

African Union chairman John Kufuor is due in Kenya on Wednesday to try and start what British Prime Minister Gordon Brown called a process of dialogue and reconciliation.

"This offers an opportunity to stop the violence and to help Kenyans unite," said Brown. Britain was Kenya's colonial power.

Pictures of the Eldoret area filmed from a helicopter by the Red Cross showed plumes of white smoke billowing from dozens of blazing homesteads on Tuesday. Young men with machetes, rocks and bows and arrows could be seen manning crude checkpoints.

Armed gangs were marching on the nearby Burnt Forest, part of the fertile Rift Valley that is home to many Kikuyus, local broadcaster NTV said.

The Eldoret attack revived memories in East Africa of the slaughter in churches of tens of thousands of people in Rwanda's 1994 genocide.

RIGGING ACCUSATIONS

Britain has called on the African Union and Commonwealth to try to reconcile Kibaki and Odinga whose parties both accuse the other of vote-rigging during the December 27 election.

Kibaki was sworn in on Sunday after official election results showed he had narrowly beaten Odinga. The EU's observer mission said the poll had "fallen short of key international and regional standards for democratic elections."

The United States first congratulated Kibaki, then switched to expressing "concerns about irregularities."

In remarks carried on the Standard newspaper's Web site, Kivuitu said he was pressured by members of the president's party who called him frequently and asked him to announce the poll results immediately.

"I do not know whether Kibaki won the election," Kivuitu was reported as saying. No independent confirmation of the reported remarks was available.

Delays announcing the final outcome had prompted allegations of rigging from Odinga's team. Four members of Kivuitu's team have said they would call for a judicial review.

The explosion of long-simmering tribal tensions from the shores of Lake Victoria to Kenya's Indian Ocean coast had displaced more than 70,000 people, police said. Reuters reporters round Kenya estimated the death toll at about 250.

Nairobi's streets had been quieter on New Year's Day than on Monday. But as dusk fell, gunfire crackled when battles between police and protesters in slum areas erupted again.

Residents feared the shadowy Mungiki gang, with roots in Kikuyu traditional rituals, and the "Taliban" gang of mostly ethnic Luos who support Odinga would launch reprisal attacks.

Vincent Ochieng nursed a gaping head wound after about 100 Mungiki youths raided the capital's ethnically mixed Kiambiu shanty town on Tuesday and hacked five people to death.

"First it was protests, then it got violent, now this is revenge," he said.

(Additional reporting by Nicolo Gnecchi, Duncan Miriri, Helen Nyambura-Mwaura, Joseph Sudah, Guled Mohamed in Kisumu; Tsegaye Tadesse in Addis Ababa; editing by Ralph Gowling)