At least 17 people are reported to have been killed in another day of violence in western Kenya, apparently linked to last month's disputed elections.
The fighting in Naivasha has forced more people to flee their homes
The victims are said to have been beaten, hacked or burned to death by mobs as fighting spread to Naivasha.
The town is about 60km (37 miles) south of Nakuru, also the scene of recent inter-ethnic fighting.
Former UN chief Kofi Annan has been holding talks to try to end the month-long political deadlock in Kenya.
He met opposition leader Raila Odinga in the capital, Nairobi, on Sunday, and called on the two rival parties to nominate officials for further talks.
Mr Annan visited the violence-racked Rift Valley on Saturday, and later said he had seen tragic, heart-wrenching scenes, and "gross and systematic abuse of human rights".
Mr Odinga accuses his rival, President Mwai Kibaki, of stealing December's presidential election.
Dozens of people are reported to have been killed in Rift Valley region in the past few days. In all at least 750 people have died since the disputed election, and about a quarter of a million have been made homeless.
Hacked to death
The fighting in Naivasha is thought to have broken out late on Saturday, descending quickly into sickening brutality, says the BBC's Adam Mynott in Nairobi.
Reports are unclear but at least nine people are said to have been hacked or clubbed to death as they tried to flee mobs with machetes.
In other cases people were locked inside their homes, which the mobs then ignited with petrol. At least eight charred bodies were said to have been recovered.
Police tried to disperse youths blocking the main road by firing over their heads. By Sunday afternoon the town was reported to be much calmer.
The mobs appeared to from the Kikuyu tribe of President Kibaki, which bore the brunt of the violence that erupted after the election.
"We have moved out to revenge the deaths of our brothers and sisters who have been killed, and nothing will stop us," said Anthony Mwangi, hefting a club in Naivasha.
"For every one Kikuyu killed, we shall avenge their killing with three," he told the Associated Press news agency.
Some of those fleeing the violence have taken shelter in some of the horticultural farms around Naivasha, on the main road between Nakuru and Nairobi, our correspondent says.
Residents of Naivasha are joining the growing number of refugees
The area's huge horticulture and flower-growing industry employs more than 20,000 people, and supplies a third of Europe's cut flowers.
Further north, Kenya's fourth biggest city Nakuru has also been the scene of deadly violence between rival Luo and Kikuyu communities.
Clashes erupted on Thursday between fighters armed with machetes, spears and bows and arrows.
There were no reports of further fighting from Nakuru on Sunday. But the ruins of torched buildings smouldered, and a reporter for news agency AFP said bodies lay in the city's deserted slums.
Meanwhile, further south in Nairobi, Mr Annan has embarked on a sixth day of talks aimed at mediating a solution to the crisis.
He met Mr Odinga, after meeting Mr Kibaki on Saturday.
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On Saturday, he visited Eldoret in the Rift Valley, scene of some of the worst post-election violence took place and spoke to refugees living in camps.
The best way to defuse the ethnic tension in the country is for politicians from the two divides to preach peace
Philip Langat, Kenya
"We saw gross and systematic abuse of human rights, of fellow citizens and it is essential that the facts be established and those responsible held to account," he said.
Fundamental changes, he added, were needed in Kenya to prevent a repetition of inter-ethnic violence.
"We cannot accept that periodically, every five years or so, this sort of incident takes place and no-one is held to account," he said.
African Union chief Alpha Oumar Konare also urged Kenya to seek a political solution to its problems.