Al Jazeera correspondent Mohammed Adow said the Kenyan government had for the first time deployed the country's military in the month of bloodshed following the December 27 polls.
A team headed by Kofi Annan, the former UN chief, on Saturday visited the heart of Kenya's ethnic fighting and vowed to push for a deal to end the violence.
He said he had seen evidence of "gross and systematic human rights abuses".
"It is essential the facts be established and those responsible be held to account," Annan told reporters in Nairobi.
"The government will have to do whatever it can to increase security."
A dusk-to-dawn curfew was imposed on Nakuru in a bid to contain pitched battles that began on Friday between tribal gangs armed with machetes and bows and arrows.
Adow said the violence had undermined hopes of a solution to the political turmoil after Mwai Kibaki, Kenya's president, on Thursday met his rival Raila Odinga, who claims the polls were rigged, in their first talks since the troubles began.
The clashes in Nakuru pit members of Kibaki's Kikuyu tribe against Luos and Kalenjins who backed Odinga.
Residents said many homes were torched and shops looted as large groups of youths armed with rocks, bows and arrows and homemade guns confronted each other across town.
About 700 people have been killed and 250,000 others forced to flee their homes since the violence began.