NAIROBI, Kenya - Kenyan President Mwai Kibaki won a second term Sunday amid allegations that the government stole the vote, sparking deadly riots that lit up the night sky as enraged youths torched homes and shouted "Kibaki must go!"

Soon after the results were announced, the government suspended live television broadcasts and the slums, home to tens of thousands of opposition supporters, exploded into fresh violence. At least 15 people were killed in fighting across the country, police and witnesses said, although the tally was likely higher.

"This country is going to turn into a war zone," said Elisha Kayugira, who ran through the Kibera shantytown searching for his sister as columns of black smoke curled above the maze of shacks and winding dirt roads.

Others were waving machetes in the air as buses and shops burned.

"These are our guns," said 24-year-old Cliff Owino, holding up a handful of rocks in Mathare, another Nairobi slum where young men set up roadblocks and built bonfires. "But a voting card is our atomic weapon."

The bloodshed was a stunning turn of events in one of the most developed countries in Africa, with a booming tourism industry and one of the continent's highest growth rates. Many observers saw the campaign as the greatest test yet of this young, multiparty democracy and expressed great disappointment as the process descended into chaos.

Raila Odinga, the firebrand opposition candidate who had been leading early results and public opinion polls, said the dispute could trigger a political crisis. He compared the country to Ivory Coast — the once stable West African nation where a 2002 coup sparked a civil war.

Elections chief Samuel Kivuitu, who read the results on live television after other media were expelled from the main vote headquarters Sunday, said Kibaki beat Odinga by 231,728 votes in the closest race in Kenya's history.

"This means Honorable Mwai Kibaki is the winner," Kivuitu said, soon after he was escorted from the counting center under armed guard. Hecklers had stopped his announcement with shouts of "This is not a police state!" and "Justice!"

But even Kivuitu had acknowledged problems with the count, including a constituency where voter turnout added up to 115 percent and another where a candidate ran away with ballot papers.

Alexander Graf Lambsdorff, the chief European Union election monitor, said the Electoral Commission of Kenya "has not succeeded in establishing the credibility of the tallying process to the satisfaction of all parties and candidates."

Kibaki was sworn in almost immediately after the results were announced, standing with his hand on the Bible in a serene ceremony at State House as his wife Lucy and dignitaries looked on.

"We have done our nation proud and set a good example for the rest of the continent," Kibaki said. "With the general election now behind us, it is time for healing and reconciliation among all Kenyans."

But even some people who voted for Kibaki had suspicions.

"I'm happy that Kibaki has won the election. I voted for him and wanted him to win," said Macharia Mwingi, 42, a taxi driver in the capital. "But I'm not ruling out election rigging."

Earlier Sunday, Odinga had called on Kibaki to concede and demanded a recount, saying the electoral commission "cannot possibly address the multiple levels of fraud administered by this administration."

Kibaki's camp urged patience for the official results, and accused Odinga's Orange Democratic Movement of being behind the violence. "ODM is responsible for all the incitement that is taking place right now," said Danson Mungatana, an official with Kibaki's Party of National Unity.

Supporters of 76-year-old Kibaki say he has turned Kenya's economy into an east African powerhouse, with an average growth rate of 5 percent. He won by a landslide in 2002, ending 24 years in power by the notoriously corrupt Daniel arap Moi, who was constitutionally barred from extending his term.

But Kibaki's anti-graft campaign has largely been seen as a failure, and the country still struggles with tribalism and poverty. After the opposition took most of the parliamentary seats in Thursday's vote, Kibaki will likely find great tests in uniting this country during his second five-year term.

Odinga, a flamboyant 62-year-old with a son named Fidel Castro, cast himself as a champion of the poor. His main constituency is Kibera, where some 700,000 people live in breathtaking poverty, but he has been accused of failing to do enough to help them in 15 years as an MP.

In recent months, Odinga has made it a priority to reach out to the country's middle class and businessmen, many of whom belong to Kibaki's tribe, the Kikuyu. Odinga belongs to the Luo tribe.

But any attempt at reconciliation was absent in the slums, where tribal clashes raged into the night and youths shouted ethnic slurs. Mercy Akinyi, 20, blamed the election for incited tribal violence.

"We have coexisted in this slum in peace," the 20-year-old said. "Now that the politicians are fighting, does that mean killing each other?"

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Associated Press writers Elizabeth A. Kennedy, Katharine Houreld, Malkhadir M. Muhumed and Tom Odula contributed to this report.