At least four people were killed in the violence, police and members of the Mungiki gang said, according to The Associated Press. The gang members burned tires and trucks, halting transportation in Nairobi and the Rift Valley town of Naivasha.
The fighting came a day after President Mwai Kibaki named opposition leader Raila Odinga as prime minister and some of Odinga's party members to a 41-member cabinet.
The naming of a coalition cabinet was critical to ending the turmoil in the east African nation following a flawed presidential election in December in which Kibaki was re-elected. The election exposed decades-old rifts in the country. The mostly ethnic-motivated violence that ensued left more than 1,000 people dead and forced 300,000 Kenyans to flee their homes.
"I want to thank you, my fellow Kenyans, for your tolerance and patience during this period," Kibaki said Sunday with Odinga at his side, Reuters reported.
"I'll do everything possible to ensure that our country Kenya is steered along the path of peace, unity and stability," said Kibaki.
Uhuru Kenyatta from Kibaki's coalition and Musalia Mudavadi of Odinga's party were named deputy prime ministers, reported Reuters.
However, Monday's fighting underscored the work that lies ahead for the coalition government in addressing the deep-seated tensions tied to ethnic, land and power disparities.
Regional police chief Philip Ndwiga said two people were shot and killed in Central province. Gang members said two others were killed in the Dandora neighborhood in the capital Nairobi.
The Kenya National Youth Alliance -- the political wing of the Mungiki gang -- released a statement blaming police for last week's killings of their imprisoned gang leader's wife and their acting leader's brother, according to the AP.
But national police spokesman Eric Kiraithe denied police involvement, saying if they were interested in the wife of the gang leader, they would have taken her to court.
The Mungiki, a quasi-religious sect described by Reuters as Kenya's version of the mafia, promote the culture of the Kikuyu, Kenya's largest tribe.
Gang members said they were approached by politicians to act as an ethnic militia during the violence following the disputed elections on Dec. 27. Kiraithe rejected those claims as well.
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