By Jeffrey Gettleman

NAIROBI, Kenya: With the results from Kenya’s closely contested elections still up in the air and evidence growing of election mischief, riots erupted across the country on Saturday.

Columns of black smoke boiled up from the slums ringing Nairobi, the capital, as supporters of Raila Odinga, the leading presidential challenger, poured into the streets to protest what they said was a plot by the government to steal the vote.

The demonstrators clashed with police officers in riot gear and tore apart metal shanties with their bare hands. The scene replayed itself in Kisumu, Kakamega, Kajiado, Eldoret and other towns across Kenya, with several people killed.

Just 12 hours before, Odinga, a flamboyant politician and businessman, had been cruising to victory, according to preliminary results. He was leading Kenya’s president, Mwai Kibaki, by about one million votes in an election that was predicted to be the most fiercely fought in Kenya’s history and perhaps the greatest test yet of this young, multiparty democracy.

But that lead nearly vanished overnight. On Saturday morning, the gap had been cut to about 100,000 votes, with Odinga still ahead, but barely, with 47 percent of the vote compared with 46 percent for Kibaki. By Saturday night, with about 90 percent of the vote counted, Odinga’s lead had shrunk to a mere 38,000 votes.

But those results may not be valid. According to Kenya’s election commission, which is considered somewhat independent from the government, at least three areas from Kibaki’s stronghold of central Kenya reported suspiciously high numbers. In one area, Kibaki received 105,000 votes, even though there were only 70,000 registered voters. In another, the vote tally was changed, at the last minute, to give the president an extra 60,000 votes. In a third area, the turnout was reported at 98 percent.

Samuel Kivuitu, the chief of Kenya’s election commission, said his officers would investigate.

“We have powers to refuse results if they have obvious defects,” he said. He delayed announcing final results until Sunday.

Kibaki’s party denied it did anything wrong and said it had simply gained many votes from areas where the president is immensely popular.

But the sudden reversal immediately ignited suspicions, especially after results showed that many members of Parliament close to the president — including the vice president, the military minister, the foreign minister and more than 10 other cabinet members — were voted out of office in a wave of seeming dissatisfaction with the government.

Several foreign observers said they feared that the government was using its muscle to swing the election and stay in power, which could be a recipe for chaos, with the results rejected by millions of people and Kenya’s cherished stability in danger of collapsing.

Kenya is one of the most developed countries in Africa, but this election has exposed its ugly tribal underbelly.

Odinga is a Luo, a big tribe in Kenya that feels marginalized from the country’s Kikuyu elite that has dominated business and politics since independence in 1963. Kibaki is a Kikuyu, and the voting so far has split straight down tribal lines, with each candidate winning big in his tribal homeland.

On Saturday, the first signs of a tribal war flared up in Nairobi, with Luo gangs sweeping into a shantytown called Mathare and stoning several Kikuyu residents. In Kibera, another huge slum, supporters of Odinga burnt down kiosks that they said belonged to Kikuyu businessmen.

“No Raila, no Kenya!” they screamed, with the fires crackling behind them.

The streets were a collage of destruction, strewn with burning tires, broken bottles, fist-size rocks and fresh shell casings from soldiers who fired in the air to scare the demonstrators off. Some men sharpened machetes on the asphalt, vowing to shed blood should Odinga lose.

Kikuyus responded by forming packs of vigilantes to patrol their neighborhoods. As night fell, the gangs waited on corners, armed with machetes and lengths of wood.

Many Kenyans seemed distressed about what was happening. In Kibera, one man in a suit guided a young girl, her face a mask of panic, through the embers of burning tires.

“Unless they announce the winner soon,” said Lionel Joseph Ochieng, a Kibera resident, “this will only get worse.”

Election officials seemed to feel the clock ticking. They said they were trying to count the votes from Thursday’s election as quickly as possible but that they have been hampered by logistical problems and a record turnout, possibly upward of 70 percent.

Both political parties declared victory on Saturday, saying that by their calculations they had won the most votes. But by 1 p.m., the election commission had counted only 8 million votes out of a projected 10 to 11 million. The hush inside the heavily guarded election headquarters was a marked contrast to the raging street battles not far away.

The foreign diplomats who initially praised the election as being free and fair were beginning to change their tone.

Michael Ranneberger, the American ambassador to Kenya, rushed to the election headquarters at midnight on Friday because he said he had heard reports about vote rigging, though he declined to provide details. He urged voters to remain calm.

“This is a time for Kenyans to come together,” he said.

The head of the European Union’s election observer mission said that several election officials in the pro-Kibaki areas of central Kenya had initially kept their poll results secret, which is against Kenyan law.

“This is something we witnessed ourselves,” said Alexander Graf Lambsdorff, chief of the European delegation. “It’s clearly disturbing.”

The European Union is also investigating the high turnouts in the Kikuyu highlands north of Nairobi, where few have broken ranks with Kibaki’s party and some areas have voted nearly 100 percent in favor of the president.

The scenario that may be unfolding is the exact one that many foreign diplomats were dreading: a questionable razor-thin margin for the president, who had been trailing in just about every pre-election poll. It is not that Kibaki, 76, is so disliked himself. He has been in government since independence and is known as a courtly gentleman and economics whiz.

But he is seen by many Kenyans as continuing an unfair political system that has favored the Kikuyu at the expense of Kenya’s 30-plus other ethnic groups. Odinga, 62, boosted his popularity by tapping into those frustrations and building a coalition of many other tribes. His party has already demanded a recount in several districts and said it will not concede defeat if it loses.