Odinga amplified his charges Wednesday, saying that the country's election commission carried out widespread fraud bigger than in "any democratic election, anywhere in the world." He told his supporters that he would take his case to Kenya's supreme court.
"For the third time in a decade, the candidate who lost the election has been declared the president," Odinga said. He has not shown any evidence of fraud.
Odinga said his supporters "won't accept it until they have answers to the disturbing questions that have been raised."
In a news conference, Odinga encouraged continued opposition to the election results and Kenyatta's presidency, saying those who accept the outcome are "prepared to live under autocracy."
Kenya is the wealthiest country in East Africa and has emerged as a pillar of stability in a fragile region, which includes war-torn neighbors Somalia and South Sudan. But Kenya remains riven by tribal rivalries that come to a head in every election cycle, largely between Kenyatta's Kikuyu tribe and Odinga's fellow Luos.
That rift predates the country's independence in 1963, and some worry that Odinga's refusal to concede will further complicate reconciliation efforts. In his reelection speech, Kenyatta urged the nation to "remember that we are brothers and sisters."
But in the wake of the 2007 elections, the International Criminal Court accused Kenyatta of fostering the wave of ethnic violence that left more than 1,000 people dead. Those charges were later dropped for lack of evidence. In his first term, however, Kenyatta did little to assuage tribal tensions, leaving many of Odinga's supporters feeling excluded and angry.
When Kenyatta was declared the winner last Friday, some young men set fire to tires in the streets of Nairobi slums and threw rocks at police. The Kenya National Human Rights Commission accused security forces of using "excessive force which is unlawful and unacceptable" against demonstrators.
Although international election monitors said last week that they saw no sign of rigging or manipulation, Kenya's election commission has not published the official result forms online, fueling speculation among Odinga's supporters that the panel is covering up some form of fraud.
On Wednesday, the European Union called for the release of those forms, saying in a statement that they "would enable all stakeholders to examine the accuracy of the announced results and point to any possible anomalies."
Meanwhile, Kenyan tax authorities attempted to raid the office of the Africa Center for Open Governance, a nongovernment group that was critical of election preparations. Officials had said that the open governance organization and the Kenya National Human Rights Commission were being suspended for not formally registering with the government. But within hours, the Interior Ministry reversed that suspension.
In a letter, the ministry said it would give the two groups 90 days to resolve "any outstanding noncompliance issues," without specifying what those issues were.
Michelle Kagari, deputy director of Amnesty International for the region including Kenya, called the suspensions "a cynical attempt to discredit human rights organizations."
But after a week of paralysis, with businesses closed and streets empty, Nairobi had come back to life. On television, tourism officials said reservations were steady. Traffic jams had returned to the city center. Even in Kibera, the sprawling slum where much of last week's violence occurred, Odinga supporters said they were ready to move on. Packed minibuses streaked through the slum's main arteries.
"We just want our lives to go back to normal," said David Kinara, 60, an Odinga supporter and a Kibera resident. "There is nothing much we can do."
"Life has to go on because if it does not, everyone is vulnerable," said Owino Kotieno, another Odinga supporter and Kibera resident. "You are vulnerable from police brutality and hooligans."
In 2013, Odinga also claimed that the election was rigged and took his case to the supreme court. After several months, he lost his case.
Rael Ombuor contributed to this report.