The clash took place when thousands of Muslim residents returning from Friday prayers started to demonstrate.
At least 16 other Kenyans were killed during the first two days of rallies called by opposition leader Raila Odinga's Orange Democratic Movement (ODM) to protest against Mwai Kibaki's re-election.
A police official said one man was slashed to death by machetes in fighting in the Mathare slum located in Nairobi, the capital, overnight,
A police commander in western Kenya said another man had died in tribal fighting, also overnight.
In the town of Narok, Masai youths killed a member of Mwai Kibaki, the president's Kikuyu tribe with a poisoned arrow.
Patrick Wambani, a police commander, said: "It is unfortunate that he met his death when he strayed into a group of armed Masai youths who were targeting members of the community in the area."
Seven new deaths were reported in the western opposition stronghold of Kisumu and the capital Nairobi, mainly in volatile slums where hundreds of protesters clashed with police, Wambani said.
Eric Kiraithe, a police spokesman, said on Friday that security forces would not allow opposition supporters on the streets for further demonstrations.
He said: "Police will be steadfast in protecting lives and property."
In the past two days, police have fired live ammunition and tear gas and beat protesters with sticks.
Prior to the nationwide protests that began Wednesday, more than 700 people died in tribal killings and clashes with police and around 260,000 others are displaced after December 27 elections in which the Kenyan opposition claims to have won.