Kenyan troops have moved into the town of Naivasha in the western Rift Valley province in an attempt to quell tribal fighting.
But hundreds of people from rival tribes, wielding machetes, clubs and rocks, confronted each other on Monday on a main Naivasha road.
Katee Mwanza, the district commissioner, said at least 22 people were killed in the Naivasha area in ethnic clashes over the past two days. Police said a least five of those were burned to death in their homes.
Naivasha, a major commercial centre, is known as Kenya's flower capital.
Kenya has been swept by ethnic violence triggered by a disputed presidential poll last month.
The death toll from a month's violence now stands at nearly 800, while at least 260,000 have been displaced since December 27.
In the normally peaceful Rift Valley town of Nakuru, a mortuary worker said on Monday that 64 corpses were lying in the morgue, all victims of the past four days of ethnic fighting. (see my friend John's blog for more photographs and information)
Violence in the Rift Valley
The police also clashed with rioters in the western city of Kisumu.
A stronghold of Raila Odinga, the opposition leader, demonstrators set several shops on fire, barricaded roads and lit bonfires across the city, witnesses said.
Police responded by firing in the air. Hundreds of people, meanwhile, fled to the city's central police station to escape the riots.
"We are trying to restore law and order in the towns," a police commander told AFP news agency. "The situation is tense at the moment."
While ethnic clashes have accompanied past Kenyan elections, the scale of the violence this year has been far worse.
It has mainly pitted ethnic groups which support the opposition because they feel marginalised, against the Kikuyu tribe of Mwai Kibaki, Kenya's president.
But the violence has taken a new twist in recent days.
Mohammed Adow, Al Jazeera's correspondent in Kenya, said: "Whereas, in the first place it was opposition supporters attacking those perceived as government supporters based on their ethnic identity, we are now seeing revenge attacks.
Human rights groups say that the latest fighting is premeditated, with those involved being trained and paid.
Muthoni Wanyeki, the executive director of the independent Kenya Human Rights Commission, told Al Jazeera: "What happened in the Rift really was organised militia activity.
"We have some of the names of training camps, we have some of the names of pay masters [but] we are still trying to trace the line of command."
She said several organisations had warned of an expected spike in violence, after militias began reorganising.
Wanyeki also called on the government to bring security to temporary camps set up for the thousands of people who fled their homes to escape the violence.
"They are still not secure," she said. "The state seems to have surplus of forces to stop people from holding rallies in Nairobi, but not have enough forces to protect the remaining camps in the Rift Valley, which is ridiculous."
The ethnic dimension to the violence has further complicated the efforts of Kofi Annan, the former UN secretary-general, who is trying to mediate and end the crisis.
Odinga, the leader of the opposition Orange Democratic Movement (ODM), who ran against Kibaki in December's election, alleges that vote rigging robbed him of the presidency.
Kibaki has said he is open to direct talks with Odinga, but that his position as president is not negotiable. Odinga says Kibaki must step down and new elections are the only way forward.
Annan met Odinga on Sunday at a hotel in Nairiobi, on the sixth day of his tour of Kenya.
On Saturday, Annan said he saw "gross and systematic human rights abuses of fellow citizens", after visits to parts of the Rift Valley.
However, his effort to end the turmoil has been undermined by the continuing violence.
Annan arranged a symbolic first meeting between Kibaki and Odinga on Thursday, but an initial signal that the opposing leaders were willing to talk was later undermined when they returned to their hardline positions.
Many Kenyans are doubtful that mediation will help.
A poll by Nation Media, the country's largest newspaper group, had only 51.6 per cent of 2,000 respondents believing Annan can resolve the crisis.
Source: Al Jazeera and agencies