Thirty Kenyans including many children have been burned to death in a church, after seeking refuge from the mounting violence over last week's elections.
Mourners have been gathering at the Kenya Assemblies of God church
A mob set fire to the church in Eldoret where many people from President Mwai Kibaki's Kikuyu tribe were sheltering.
The Kenyan government has accused supporters of opposition leader Raila Odinga of carrying out "ethnic cleansing" against the Kikuyu.
Both President Kibaki and Mr Odinga have called for the killing to stop.
An estimated 250 people have died in the violence that erupted following the controversial re-election of President Kibaki, according to police and journalists across the country.
President Kibaki, who was swiftly sworn in on Sunday amid opponents' accusations that the poll was rigged, said political parties should meet immediately and publicly called for calm.
But Mr Odinga said he would only hold talks once the re-installed president "publicly owns up that he was not elected".
EU observers said the poll "fell short of international standards", and four Kenyan election commissioners have joined calls for an independent judicial body to re-examine the process.
The government has denied any irregularities.
About 400 people were said to be taking refuge in the Kenya Assemblies of God church when the attack took place at about 1000 (0700 GMT).
A pastor from the church, Jackson Nyanga, told the BBC that many of the people were beaten before the building was set on fire.
"After torching the church, children died - around 25 in number - four elderly people. And our men and our people who tried to confront them were injured," he said.
Eldoret, in the Rift Valley, has witnessed some of the worst violence since last Sunday's controversial poll and has a history of inter-ethnic tension.
Correspondents say that over the past few days hundreds of Kikuyus in the Eldoret area have been taking shelter in churches and around the town's police station.
Eldoret resident Bernard Magamu told the BBC News website that many houses and businesses have been torched, and that roads in and around the town are closed.
Mwai Kibaki (pictured): 4,584,721 votes
Raila Odinga: 4,352,993
Kalonzo Musyoka: 879,903
"People are still fearful. It's hard. People are really scared," said Mr Magamu, adding that local hospitals were struggling to cope with the high number of casualties.
The Kenyan Red Cross said that at least 70,000 people have been displaced in the Rift Valley area as a result of the unrest, describing it as "a national disaster".
Alfred Mutua, spokesman for the Kenyan government, accused Mr Odinga's supporters of a systematic campaign of ethnic violence.
"Raila Odinga's supporters... are engaging in ethnic cleansing and they are not doing it in a haphazard manner, they're doing it in a very well organised, calculated manner... attacking in military precision," he told the BBC World Service.
UK Prime Minister Gordon Brown has again urged Kenya's political leaders to talk, and said: "The violence must be brought to an end."
EU observers said the country's election was flawed.
"They were marred by a lack of transparency in the processing and tallying of presidential results, which raises concerns about the accuracy of the final results," the EU team said in a statement.
According to the EU, in at least two constituencies - Molo and Kieni - the results that were announced did not reflect the number of votes cast.
EU observers say they heard the voting figures being announced in Molo itself, but when the same results were announced again in Nairobi, the number of votes for Mr Kibaki was significantly higher - by 25,000.
Four of the 22 Kenyan election commissioners have also expressed doubts about the veracity of the figures giving President Kibaki victory by 200,000 votes.
But Finance Minister Amos Kimunya denied his party, the ruling PNU, or the government had been involved in rigging the poll.
He told the BBC: "I have no evidence that they were rigged. Anyone who has any information that they were rigged in one constituency or the other, or overall, let them subject it through the legal process."
Mr Kibaki was declared the winner on Sunday after a controversial three-day counting process.
His challenger, Mr Odinga, said he was robbed of victory by alleged fraud.