Fresh riots broke out on the streets of Kenya's capital Nairobi today after an opposition MP was murdered by gunmen at his home.
As unarmed supporters of Mugabe Were gathered outside his house, police fired tear gas at them.
Mr Were was one of several members of the opposition Orange Democratic Movement who won seats in December in a vote held at the same time as the disputed presidential election which originally sparked the current violence.
He was shot as he arrived in his car at his home in a Nairobi suburb.
ODM leader Raila Odinga said: "We suspect the foul hands of our adversaries."
Mr Odinga said he too would join mourners outside Were's home, where dozens of people manned burning tyre barricades and uprooted telephone posts. "No Raila, no peace!" they yelled.
Police said they did not yet know if the political turmoil had motivated the slaying.
"We are treating it as a murder but we are not ruling out anything, including political motives," a spokesman said. "We are urging everyone to remain calm."
Groups of armed youths also began gathering in the capital's Mathare and Kibera slums after the shooting.
A resident of Nairobi's Kibera slum, Teddy Njoroge, said houses were being set on fire near an unofficial border dividing members of President Mwai Kibaki's Kikuyu tribe from those Mr Odinga's Luos. Flames and smoke rose from one area of Kibera.
"They have decided to revenge this MP," Mr Njoroge said.
Mr Kibaki condemned the killing and appealed to Kenyans to maintain peace and avoid drawing premature conclusions. In a statement, he promised police would act swiftly to ensure the perpetrators were dealt with severely.
The killing came as thousands of machete-wielding youths from both Kikuyu and Luo tribes hunted each other down in western Kenya's Rift Valley, burning homes, blocking roads with blazing tyres and clashing with police who appeared overwhelmed.
At least 90 people were killed there over the weekend. The death toll since the disputed elections on December 27 is now more than 800.
US presidential hopeful Barack Obama, the Democratic senator whose father was Kenyan, appealed for peace on Nairobi's Capital FM radio station.
"Now is the time for all parties to renounce violence. Now is the time for Kenyan leaders to rise above party affiliations and past ambitions for the sake of peace," he said.
In the town of Naivasha, two police helicopters fired on a crowd of looters and protesters.
Crowds set fire to homes and thousands of looters smashed shop windows in the town. Five police officers fired into the air but were unable to control the mob of about 5,000. Naivasha's police chief tried to calm the crowd, but was pelted with stones and fled in his car.
The two helicopters then flew over the crowd and opened fire, sending people running in panic.
In addition to the looting in Naivasha, a local reporter saw a mob of Kikuyus stone to death two Luos, a retired prison warden and a businessman, an a flower estate on the outskirts of town. Earlier, Kikuyus stoned to death a Luo man trying to retrieve his belongings from another flower estate.
Outside Naivasha Country Club, police were trying to rescue hundreds of Luos from a mob of Kikuyus armed with machetes and clubs inset with nails.
"We're trapped," said Rose Achieng, who fled with her two children when looters ransacked her home on Sunday. She and hundreds others had sought refuge next to the police station, beside the road outside the country club.
Police, apparently worried they could not protect them, started ferrying them in trucks to the town's walled prison compound, where more than 1,000 refugees already had gathered.
"If you stay we will kill you," Kikuyus yelled. When they surged forward, brandishing machetes, police fired into the air.
In Kisumu town, where columns of smoke rose from burning homes yesterday, police took away one charred body.
"We didn't waste time, we had to kill him," said Stanley Ochieng, 25. He said they stoned the man, slashed him with machetes, then threw him to burn on their roadblock of burning tires because he was Kikuyu.
Hundreds of machete-wielding youths lobbed stones at police, who responded by firing live bullets into the air.
Mr Kibaki and Mr Odinga blame each other for the violence, which has driven 255,000 people from their homes. The two men have traded accusations of "ethnic cleansing".
Human rights groups and officials say the violence has become organised.
Former UN Secretary-General Kofi Annan, who is trying to mediate in the dispute, announced in a statement that the "dialogue process" to help resolve the dispute will start today.