A 3,000-strong mob armed with bows and arrows, spears, clubs and machetes has murdered a police officer in the violence-hit Rift Valley region of western Kenya.

The lynching took place near Ainamoi, after the officer was accused of wounding a civilian when police fired on protesters yesterday.

Peter Aliwa, a police commander, said it was the first reported killing of a policeman in the violence that has raged in Kenya since disputed elections a month ago. “The police officer injured three attackers before he was overpowered and lynched on the spot,” he said.

The police have shot scores of people in riots and protests accross Kenya since Raila Odinga, the opposition leader, accused President Kibaki of rigging his re-election on December 27.

Yesterday’s protests that were broken up by police gunfire came in response to the death of David Kimutai Too, an opposition MP, who was shot by a traffic policeman at a road block in the nearby town of Eldoret.

It appears that the killing was a crime of passion rather than a political assassination but by shooting the politician, who was surreptitiously dating his girlfriend, the policeman sparked another wave of protest and violence.

Mr Too was the second opposition MP to be shot dead in a week and protestors assumed the murders were linked to the otribal and political turmoil that has seen almost 900 killed and at least 300,000 forced from their homes.

Ban Ki-moon, the UN Secretary-General, arrived in Nairobi today to help negotiate a peaceful resolution to the electoral crisis.

“I’m reasonably encouraged by the commitment and the willingness of all the political leaders, as well the community leaders who are now looking at the possibility of resolving this issue though dialogue and peaceful means,” he said.

“The killing must stop. The violence must end for the sake of the Kenyan people and for the sake of Kenya."

“You have lost already too much in terms of national image, in terms of economic interests. You lost many tourists, this is a very unfortunate situation for a country which has been enjoying freedom and security and stability.”

Kofi Annan, the previous head of the UN, is also in the Kenyan capital attempting to broker talks between Mr Kibaki and Mr Odinga.

Mr Annan warned yesterday, while talks were suspended after rioting greeted Mr Too’s death, that it was fast becoming impossible for aid agencies to operate in the east African nation marred by bloodshed.

Kenya’s security forces have begun a crackdown after a month of chaos and killings but members of the opposition Orange Democratic Movement say the brutal activity of the security forces has targeted those protesting against the incumbent president.

Helicopters were scrambled to put down rioting by the Kikuyu, who support President Kibaki, in Naivasha this week. Crowds were dispersed by rubber bullets, but opposition supporters claim that their protests were quelled more brutally.

At least two civilians were shot dead by police who were trying to keep an angry mob away from the Eldoret police station after the murder of Mr Too yesterday.

“The shooting was careless and there was no provocation,”, a witness in Eldoret told Reuters. “The Kikuyus are allowed to demonstrate and kill people ... But when we in the west demonstrate they sent people to kill us straight away.”

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