Clashes between machete-wielding mobs erupted in western Kenya on Monday after dozens were killed in weekend violence that pushed the estimated death toll since last month's disputed presidential election to more than 800.

Police provide armed escort for a truck being used to carry families fleeing from their neighbourhood in Naivasha on Monday because of threats by members of opposing tribes. ((Roberto Schmidt/AFP/Getty Images))

In the Rift Valley resort town of Naivasha, about 90 kilometres northwest of Nairobi, hundreds of people from rival tribes confronted one another on a main road.

The crowds retreated only when a handful of police between them fired live bullets into the air, the Associated Press reported.

The fighting began after President Mwai Kibaki's Dec. 27 re-election, which opposition leader Raila Odinga and his supporters say was rigged. International and local election observers have said there were significant problems with the vote.

The violence has featured battles between armed police and protesters in the western opposition heartland and in Nairobi's slums, as well as politically motivated clashes between rival ethnic groups.

Some 250,000 Kenyans have been forced from their homes out of fear of targeted attacks from tribes aligned with Odinga's Luo ethnic group and reprisal attacks from Kenya's influential Kikuyus. Kibaki is a Kikuyu, which prompted mobs to target the president's suspected supporters immediately after his Dec. 30 swearing-in ceremony.

At least 22 people were killed in Naivasha over the weekend, said district commissioner Katee Mwanza. Nineteen of them were Luos whom a gang of Kikuyus chased through a slum and trapped in a shanty that they set on fire, said police commander Grace Kakai.

The others were hacked to death with machetes, a local reporter told the Associated Press.

Similar clashes were reported in Nakuru, the regional capital of the Rift Valley, where an unnamed morgue worker said 55 bodies were counted Sunday after battles between tribes broke out earlier in the week.

National police commissioner Hussein Ali told reporters in Nairobi that police had arrested 159 people in Nakuru and Naivasha "for possession of crude weapons and for suspected involvement in the murders." He also said 95 people were arrested in Nairobi, but gave no details.

The deaths present new challenges to former UN secretary general Kofi Annan, who is in Nairobi attempting to mediate a solution to the political crisis.

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 only new elections will bring peace.