NAIROBI, Kenya — Opposition supporters hurled stones, overturned kiosks and set them ablaze Thursday, but riot police beat them back with tear gas and water cannons in another day of tribally charged chaos after Kenya's disputed presidential election.

Opposition leaders were forced to call off what had been billed as a "million-man march" after police and soldiers blocked access to Uhuru Park, a large public plaza whose name means "freedom" in Swahili. But supporters vowed to continue violent protests until the president, Mwai Kibaki, stepped down for allegedly stealing last week's election.

There were few deaths reported in the protests. But Kenya was slipping deeper into uncertainty as Kibaki and challenger Raila Odinga rejected international calls for a political compromise to end the worst ethnic bloodletting in decades in this once-stable African nation.

In Washington, the State Department announced that Jendayi Frazer, the assistant secretary of state for Africa, will fly to Kenya to meet Kibaki and Odinga.

Kibaki claimed a second five-year term despite credible reports of fraud in the ballot count from the vote Dec. 27. The outcome has sparked a nationwide wave of violence directed mainly at Kibaki's tribe, the Kikuyu, whose control over politics and business long has fueled resentment among many of Kenya's 41 other tribes.

Human rights groups say that Odinga supporters — including many from his own tribe, the Luo — are killing Kikuyus. The death toll so far is 300, according to estimates by rights groups, and 200,000 people have been forced to flee their homes, the Kenya Red Cross Society said.

Archbishop Desmond Tutu of South Africa, a Nobel peace laureate, arrived in Kenya to serve as a mediator. He said after talks with Odinga that Odinga was willing to negotiate.

In public, however, Odinga continued to call for Kibaki's resignation.

"You want me to share power with a thief?" he said.

His claims of election fraud were bolstered by Kenya's attorney general, who called for an independent review of the results. Amos Wako, whom Kibaki's predecessor appointed, said "a proper tally . . . should be undertaken immediately on a priority basis by an agreed and independent person or body."

In Nairobi's ethnically mixed slum of Mathare, dozens of families are sleeping in the open air outside a police outpost, away from clashes between Kikuyus and Luos.

On Thursday morning, residents said, a mob of young Luo men rampaged through the fetid dirt alleyways, attacking Kikuyu women. Some Kikuyu men appeared and chased the Luos with machetes, caught one of them and hacked him in the head. A few hours later, his dead body was still lying in the dirt. His head had been crudely covered with bits of plastic and his shoes had been stolen, leaving dirty white socks covering his feet.

"Kibaki has all the nation's blood on his hands," said Mike Obutho, a 30-year-old Luo. "This is going to go on and on."

The crisis was beginning to squeeze neighboring countries, which rely on Kenya's roads to import fuel and other vital commodities from Mombasa, the most important port in East Africa. Fuel supplies are dangerously low in Uganda and Burundi, and neighboring Rwanda has begun rationing, officials said.