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International pressure mounted Wednesday on Kenya's leaders to bring an end to postelection violence that has shaken the country and killed more than 275 people, including dozens burned alive as they sought refuge in a church.

The killing of up to 50 ethnic Kikuyus Tuesday as they sheltered in a church in the Rift Valley city of Eldoret fueled fears that ethnic conflicts were deepening in what has been one of Africa's most stable democracies.

The U.N. cited Kenyan police as saying 70,000 people had been displaced in five days of violence. Around 5,400 people also have fled to neighboring Uganda, said Musa Ecweru, that country's disaster preparedness minister. Several hundred people also have fled to Tanzania, officials there said.

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Much of Nairobi was quiet and deserted Wednesday, though clashes continued in the city's giant Mathare slum.

Livingstone Wesonga said his wife lost their fifth child on Tuesday night after complications during the delivery. Vigilante groups roaming the streets kept the family penned in their home and no ambulance or doctor was willing or able to come.

Asked why he had not fled with his family, Wesonga said: "Where can I take them? Every place is not safe because this thing is spreading."

Government spokesman Alfred Mutua downplayed the violence, saying it had only affected about 3 percent of the country's 34 million people. "Kenya is not burning and not at the throes of any division," he said.

Mutua said the security forces had arrested 500 people since skirmishes began.

President Mwai Kibaki was inaugurated for a second term Sunday, but his rival Raila Odinga says the poll was rigged.

The head of the country's electoral commission, Samuel Kivuitu, said he had been pressured by both sides to announce the results quickly — and perhaps wrongly. The country's oldest newspaper, The Standard, on Wednesday quoted Kivuitu as saying, "I do not know whether Kibaki won the election."

In a joint statement, Secretary of State Condoleezza Rice and Britain's Foreign Secretary David Miliband also said there were "independent reports of serious irregularities in the counting process."

The pair welcomed news the African Union would send its chief, Ghanaian President John Kufuor, to mediate the conflict. The AU's spokeswoman Habiba Mejri-Cheikh said Kufuor was expected in Kenya Wednesday, but Kufuor's press office said the leader had canceled the visit. They gave no explanation.

Rice and Miliband called "on all political leaders to engage in a spirit of compromise that puts the democratic interests of Kenya first."

"The immediate priority is to combine a sustained call from Kenya's political leaders for the cessation of violence by their followers with an intensive political and legal process that can build a united and peaceful future for Kenya," the statement said.

On Tuesday, Kibaki called for a meeting with his political opponents — a significant softening of tone for a man who vowed to crack down on rioters.

But opposition candidate Raila Odinga refused, saying he would meet Kibaki only "if he announces that he was not elected." Odinga accused the government of stoking the chaos, telling The Associated Press in an interview that Kibaki's administration "is guilty, directly, of genocide."

In Nairobi's slums, which are often divided along tribal lines, rival groups have been fighting each other with machetes and sticks as police use tear gas and bullets to keep them from pouring into the city center. The capital has been a ghost town for days, with residents stocking up on food and water and staying in their homes.

In Mathare, mothers clutching wide-eyed infants and suitcases were evacuated by riot police while angry youths armed with machetes and axes heaped abuse on the police as the slum burned.

"All you do here is come to pick up bodies," shouted Boniface Shikami.

Several threw rocks toward the police vehicle, and officers fired in the air before a patrol truck skidded around a corner to try to separate battling supporters of Odinga and Kibaki.

As shopkeepers battled with flames leaping through their corrugated iron roofs, a dazed woman clutching a kitten wandered through the smoke.

"They have burned down my house and all I have now is my cat," wailed Hannah Warigui.

John Okello, a doctor, said clinics around the city were running short of basic materials like gauze because so many people have been arriving with machete wounds. He said the city's main Nairobi Hospital was trying to ferry supplies to the clinics.

The people killed in Eldoret, about 185 miles northwest of Nairobi, were members of Kibaki's Kikuyu tribe.

The Kikuyus in Eldoret had fled to the Assemblies of God Church on Monday night, seeking refuge after mobs torched homes. Video from a helicopter chartered by the Red Cross showed many homes in flames and the horizon obscured by smoke. Groups of people were seen seeking sanctuary at schools and the airport, while others moved into the forest.

On Tuesday morning, a mob of about 2,000 arrived at the church, said George Karanja, whose family had sought refuge there.

"They started burning the church," Karanja said, his voice catching with emotion as he described the scene. "The mattresses that people were sleeping on caught fire. There was a stampede, and people fell on one another."

Karanja, 37, helped pull out at least 10 people, but added, "I could not manage to pull out my sister's son. He was screaming 'Uncle, uncle!' ... He died." The boy was 11.

Up to 50 people were killed in the attack, said a Red Cross official who spoke on condition of anonymity because her name would identify her tribe, and she feared reprisal. Even first aid workers were stopped by vigilantes who demanded their identity.

Karanja said his two children raised their hands as they left the church and they were beaten with a cane, but not killed. His 90-year-old father was attacked with a machete, but survived, he said.

"The worst part is that they were hacking people and then setting them on fire," he added.

The attackers saw Karanja saving people and began stoning him, he said. Karanja said he ran and hid — submerging himself in a pit latrine outside the church property. He stayed there about 30 minutes until he heard people speaking Kikuyu, he added.

The Kikuyu, Kenya's largest ethnic group, are accused of using their dominance of politics and business to the detriment of others. Odinga is from the Luo tribe, a smaller but still major tribe that says it has been marginalized.

There are more than 40 tribes in Kenya, and political leaders have often used unemployed and uneducated young men to intimidate opponents. While Kibaki and Odinga have support from across the tribal spectrum, the youth responsible for the violence tend to see politics in strictly ethnic terms.

The prospect of even more violence is ahead. Odinga insisted he would go ahead with plans to lead a protest march in the capital Thursday. The government banned the demonstration, but Odinga said: "It doesn't matter what they say."

Kibaki, 76, won by a landslide in 2002, ending 24 years of rule by Daniel arap Moi. Kibaki is praised for turning the country into an east African economic powerhouse with an average growth rate of 5 percent, but his anti-graft campaign has been seen as a failure, and the country still struggles with tribalism and poverty.

Odinga, 62, cast himself as a champion of the poor. His main constituency is the Kibera slum, where some 700,000 people live in poverty, but he has been accused of failing to do enough to help them in 15 years as a member of parliament.