Nairobi  - A United Nations expert on extrajudicial and summary executions on Monday begins a ten-day mission to investigate the killings that followed disputed December 2007 elections in Kenya, the UN said.

Philip Alston, who was invited by the Kenyan government, is to visit some of the hotspots of violence, including the capital Nairobi and Eldoret, where dozens died when a church was burned to the ground.

His mandate is to report on the killings and look at "the underlying causes that might have prevented effective legal action to prosecute and punish those responsible."

Alston will wrap up his visit on February 25 and hand in a report to the Human Rights Council.

Around 1,500 people died in clashes between rival tribes affiliated to political parties after presidential elections at the end of December 2007. Hundreds of thousands were displaced.

The trouble came after Orange Democratic Movement leader Raila Odinga's accusation that President Mwai Kibaki's Party of National Unity had rigged the elections.

Calm returned after several months and a deal negotiated by former UN secretary general Kofi Annan saw the creation of a power-sharing government, with Odinga sworn in as prime minister in April.

Kenyan MPs on Thursday failed to pass a bill to create a special tribunal to try politicians and businessmen accused of orchestrating the violence.

Annan said he was disappointed with the decision, and hinted he would refer the case to the International Criminal Court (ICC) in The Hague.

A probe into the violence recommended that if a local tribunal was not set up by March 1, Annan should hand over an envelope containing the names of the accused to the ICC. (dpa)