At least four people have died after mobs torched houses in a slum in the Kenyan capital Nairobi, after the killing of an opposition MP nearby.
Police are struggling to control looters in Naivasha
Mugabe Were, from beaten presidential candidate Raila Odinga's ODM party, apparently died in violence triggered by disputed elections last month.
Meanwhile, towns in the Rift Valley are witnessing fresh inter-ethnic fighting.
Army helicopters fired on a mob of ethnic Kikuyus attacking Luo refugees trying to flee the town of Naivasha.
They used tear-gas canisters and rubber bullets, causing the crowds to flee in panic.
Police on the ground had been unable to control the mob, said to number thousands of people, which was looting and burning buildings in the town.
Members of President Mwai Kibaki's Kikuyu tribe have been fighting with Luos and Kalenjins who backed Mr Odinga in last month's election.
As the violence continues, members of the government and opposition have begun arriving at the County Hall in Nairobi for talks to be mediated by former UN chief Kofi Annan, scheduled to begin on Tuesday afternoon.
Eyewitnesses in Kibera, where Mr Were died, said houses were on fire near a railway line which divides ethnic groups in the slum.
Four people were killed by machetes and arrows, and another three deaths were suspected.
In other violence:
- At least one demonstrator is killed as police fire tear gas on about 100 opposition supporters in the western port city of Kisumu
- Police fire on opposition supporters armed with bows and arrows in Cheptiret near Eldoret, in the Rift Valley, killing three, AFP news agency reports
- Six people died in overnight clashes in Eldoret, AFP says
- Parts of the railway line to Uganda are torn up
Mr Were is the first leading politician to have died amid violence that has gripped Kenya since December's poll.
Two gunmen shot Mr Were as he drove up to the gate of his house in the capital just after midnight, Kenya police spokesman Eric Kiraithe was quoted by the Associated Press news agency as saying.
"We are treating it as a murder but we are not ruling out anything, including political motives. We are urging everyone to remain calm," he said.
Mr Were, who represented Nairobi's Embakasai district, won a seat in the 27 December legislative election, which was held at the same time as the presidential vote.
Mr Kibaki condemned the killing, but urged Kenyans not to jump to conclusions about who had carried it out.
Mr Odinga pointed the finger at the government.
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"We suspect a foul hand of our adversaries in this," he said.
Kofi Annan has a lot to achieve, as large swathes of the country are beyond the control of security forces. Kibaki and Raila owe Kenyans an answer
"We hope and expect that investigations are going to be carried out by the law enforcement agencies, but as you can see, the country is drifting into a state of anarchy."
ODM spokesman Salim Lone called on people "to be peaceful and to only respond to this kind of violence by shunning violence".
Police fired tear gas at Mr Were's compound in Nairobi to disperse protesters outside.
Mr Odinga accuses Mr Kibaki of stealing the vote and has refused to recognise the result.
Analysts warn a cycle of violence is emerging amid the political impasse, where the pattern of attacks is followed by reprisals.