U.N. Secretary-General Ban Ki-moon flew into Kenya on Friday to provide heavyweight diplomatic clout for efforts to end a month of post-election turmoil in which more than 850 people have been killed.

African leaders at a summit in neighbouring Ethiopia attended by the U.N. head have called for urgent action to stop the bloodletting, which has turned one of the continent's more stable nations and best economies into its most pressing crisis.

Ban arrived from Ethiopia in the morning to meet predecessor Kofi Annan, who is spearheading mediation efforts in Nairobi, as well as opposition leader Raila Odinga and civil society representatives, U.N. officials said.

He told the 53-nation African Union summit on Thursday the violence in Kenya threatened to "escalate to catastrophic levels" and called on President Mwai Kibaki and Odinga to do everything possible to resolve the crisis.

"The aim of the visit is to offer support to the Annan-led panel and be briefed by the U.N. country team on the humanitarian crisis," a U.N. official in Nairobi said.

More than 300,000 Kenyans are living as refugees.

Kenya descended into a spiral of political and ethnic killing after Kibaki's disputed re-election on December 27.

Odinga says Kibaki stole the vote, Kibaki says he is the legitimately-elected leader, while international observers said the count was so chaotic it was impossible to tell who won.

Media and civil society groups urged leaders to bury their differences for the sake of national peace.

Even so, "there's no way we can buy back the lives of the dead," wrote columnist Lucy Oriang' in the Daily Nation.

"FORCES OF DEATH"

The unrest has taken the lid off decades-old divisions between tribal groupings over land, wealth and power, dating from British colonial rule and stoked by Kenyan politicians during 44 years of independence.

"The country has been battered and traumatised so much," wrote the Nation in an editorial. "The malevolent forces of death must be stopped in their tracks."

The United States and European countries have pledged their support for Annan's mediation efforts. Donors have said aid programmes to Kenya are under review.

A group of mostly European donors has suspended future payments on a good governance and law enforcement programme in light of the current crisis, Denmark's ambassador said.

Many in the country fear what will happen if Annan fails to clinch some sort of power-sharing deal.

Fresh protests, in which witnesses said at least two people were killed, broke out on Thursday after a police officer in the Rift Valley town of Eldoret shot dead an opposition legislator, the second killed in a week.

The officer was being arraigned in court on Friday.

Police have said they are treating the killing as a "crime of passion" rather than a political act, but Odinga condemned it as a deliberate assassination.

"This gentleman of course was with some lady, but is that itself a crime? How can they come to conclusions before any investigations?" Odinga told Reuters.

Soldiers fired into the air to disperse angry mobs in Eldoret after the MP's killing. Hospital sources said at least 20 people were wounded in the fighting.

Lying in a hospital bed with a bullet still lodged in his back, mason James Musire says he was walking back from a school meeting when security forces shot him. "I tried to put up my hands in surrender, but they just shot," he said.

Protests also erupted in the pro-opposition western town of Kisumu. Youths burned tyres and blocked roads with rocks.