Yasuyoshi Chiba, Afp, Getty Images
A supporter of Raila Odinga demonstrates in front of a burning business at Kibera in Nairobi, Kenya, on Saturday.

KIBERA, Kenya — Machete-wielding youths rioted in Kenya on Saturday as each party vying for the presidency declared its candidate the winner, threatening an election that initially was praised by international observers.

In early results, challenger Raila Odinga had led President Mwai Kibaki by several hundred thousand votes, but by late Saturday, Odinga's lead had dwindled. Amid opposition accusations of fraud, ethnic riots exploded in several cities.

In Odinga's strongholds, supporters from his Luo tribe looted businesses and set fire to shops and houses belonging to Kikuyus, the tribe associated with Kibaki.

Police fired tear gas as youths rioted and chanted anti-Kikuyu slogans in the Kibera slum area of Nairobi after Odinga's lead in the count was whittled down in an election that is crucial to consolidate this East African nation's young democracy.

Violence also was reported in Kisumu, coastal Mombasa and other towns.

By late Saturday, the Electoral Commission of Kenya put Odinga ahead of Kibaki by only 38,000 votes, with 191 of 210 constituencies counted. Earlier, Odinga had racked up a substantial lead. The latest tallies were 3,880,053 for Odinga and 3,842,051 for Kibaki.

Earlier, the opposition Orange Democratic Movement had declared Odinga the winner and called on Kibaki to concede.

"In view of the growing anxiety and restlessness in the country over the extended delay ... we now call upon the outgoing president to acknowledge and respect the will of the Kenyan people and concede defeat," said Musalia Mudavadi, the party's candidate for vice president.

Kibaki's Party of National Unity countered by releasing its own count, putting the president ahead and declaring him the winner.

Kenya's last presidential election, in 2002, was seen by analysts as its first real democratic vote, although multiparty elections were reintroduced in 1992. If Kibaki loses, it would be the first time an incumbent president has been voted out in Kenya, and one of only a few cases in sub-Saharan Africa.

Black smoke hung over Kibera and flames shot into the air as youths rampaged Saturday, destroying Kikuyu property. Burned tires, charred planks of wood and sheets of iron littered the road.

Opposition supporters were breaking up shop kiosks, shouting, "No Raila, No Kenya; No Raila, No Peace!" and "Kibaki must go!" Police pursued them along the arrow alleys with guns raised.

"They are delaying the results to steal, and we all know that," said one of the protesters, George Otieno, 33. "There is a plan and it's to return Kibaki to State House, and that will not happen," he said referring to the presidential residence. "We voted peacefully, and we should get fair results."

One woman was slumped against the open door of a white saloon car, weeping after youths armed with "pangas," or machetes, burned down her small clothing kiosk and stole all her stock.

Tensions rose after Odinga opened up a strong lead in unofficial counting announced on local television Friday and Kibaki later began to close the gap as the count dragged on, fueling opposition suspicions that the vote was being rigged.

In the lead-up to the elections, the opposition accused the government of preparing to rig the vote, a claim Kibaki strongly denied.

Both parties called on the panel to speed its count, but commission chief Samuel Kivuitu declared that he would not be rushed and indicated that final results would be announced Sunday.

Kenya was ruled for nearly four decades by the Kenya African National Union, 24 of those years under then-President Daniel Arap Moi, who tortured and imprisoned political opponents, including Odinga. Kibaki won power in 2002, when Moi constitutionally was barred from running.

In the last five years, Kibaki has delivered economic stability, free primary education and average 5 percent growth, but opponents say he has failed to fight corruption. Odinga, a businessman who campaigns in a red Hummer and styles himself as the champion of the poor, has promised to distribute wealth more equally.