Former UN chief Kofi Annan has opened talks with Kenya's rival president and opposition leader, to try to end weeks of violence linked to disputed polls.
Mr Annan, flanked by President Mwai Kibaki and ODM party leader Raila Odinga, urged the two men to do "whatever possible" to restore calm.
Mr Annan said short-term political issues could be solved in four weeks, but full talks could take a year.
The talks came after the death of an opposition MP sparked fresh violence.
At least nine people died on Tuesday in outbreaks of violence after Mugabe Were, from Mr Odinga's ODM party, was shot on Monday night.
Opening the talks, Mr Annan said: "There is only one Kenya. We all have multiple identities but I hope you see yourselves as Kenyans first."
He warned that the crisis was having a "profound and negative impact" on the country, and urged the two leaders to take the talks seriously or risk losing aid.
Speaking after Mr Annan, Mr Odinga stressed that the resolution of the "deeply flawed" results of the presidential elections needed "most urgent attention".
Mr Odinga has launched street protests against Mr Kibaki's victory in the polls, during which international observers noted several irregularities.
"I seek to be president of all Kenyans," he said.
"I will leave no stone unturned... to ensure that... Kofi Annan's mediation mission between the PNU [Kibaki's Party of National Unity] and the ODM succeeds. And I emphasise PNU and ODM - not PNU 'government'."
President Kibaki said he strongly condemned incidents of violence, and would "implement stern measures" against "those who disrupt the peace".
He pledged to support mediation attempts, provide more police stations and create a fund for victims of the violence.
US Secretary of State Condoleezza Rice expressed support for the mediation process and said the situation in Kenya was "deeply concerning".
Mr Were is the first leading politician to have died amid violence that has left at least 800 people dead.
A spokesman for the police said they were treating the incident as a murder, but were not ruling out political motives.
Earlier, Mr Kibaki condemned what he described as the "heinous" killing.
Mr Odinga said his party suspected the "foul hand of our adversaries" in the attack.
Outside Mr Were's Nairobi home, tear gas was fired at mourners and supporters who reportedly taunted police.
Elsewhere, at least two people died in the Rift Valley town of Naivasha, where army helicopters fired tear gas and what they said were rubber bullets at a mob of ethnic Kikuyus attacking Luo refugees trying to flee the town.
In Nairobi, at least seven people died in the slums of Kibera and Mathare as crowds of youths from rival ethnic communities fought each other with machetes and clubs.
Some analysts fear a cycle of ethnically-driven revenge and reprisal attacks has taken on a momentum of its own.
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Members of President Kibaki's Kikuyu tribe have been fighting with Luos and Kalenjins, who backed Mr Odinga in the 27 December poll. The initial violence was characterised by mob attacks largely targeting Mr Kibaki's Kikuyu ethnic group.
Kofi Annan has a lot to achieve, as large swathes of the country are beyond the control of security forces
And ODM protesters, often armed with machetes, were shot at by police.
But in recent days, Kikuyu reprisal attacks have become increasingly common.
Ethnic divisions over land, wealth and power have dogged Kenyan politics since independence in 1963. There is widespread resentment over the economic power some Kikuyus hold.
Mr Kibaki says Mr Odinga should fight his case in the courts and has offered to form a government of national unity.
Mr Odinga has refused to recognise Mr Kibaki as president and called for a re-run of the poll.