Kenyan police have killed at least 11 people in a crackdown on protests over the re-election of Kenyan President Uhuru Kenyatta.
Riots have been reported in the western city of Kisumu and the capital, Nairobi.
The bodies of nine young men shot dead overnight in Nairobi's Mathare slum have been brought to the city morgue.
Police say they were shot dead during anti-looting operations.
Mr Kenyatta, in office since 2013, took 54.3 percent of votes, ahead of his rival Raila Odinga, with 44.7 percent.
After the announcement, Mr Kenyatta called for unity, telling opposition supporters: "I reach out to you... We are all citizens of the same republic".
But the opposition rejected the results even before they were declared, calling the process a "charade".
However, it has been endorsed by international observers. Mr Kenyatta said they had ensured a "free, fair and credible election".
Angry protests started in the city of Kisumu - an opposition stronghold - and in various slums of the capital Nairobi, including Kibera, where businesses are said to have been attacked.
Earlier, Mr Odinga's supporters said he had won, and published their own figures. The electoral commission said this was "illegal and premature", and said basic mathematical errors had been made.
Many observers fear a repeat of the violence after the disputed election 10 years ago, when more than 1100 Kenyans died and 600,000 were displaced.
Mr Kenyatta has urged peace. "We have seen the results of political violence. And I am certain that there is no single Kenyan who would wish for us to go back to this," he said.
Ahead of the results, Mr Odinga had called on his supporters to remain calm, but added that he did not control anyone, and that "people want to see justice".
Before the results were read, one of the leaders of the opposition Nasa alliance, Musalia Mudavadi, said concerns about the poll had not been adequately addressed.
Nasa has complained of fraud and hacking, and called for access to the election commission's data servers. The commission has defended its process and says the results published are accurate.
Another top opposition official, James Orengo, said the coalition would not be taking its issues to court, raising the spectre of street protests.
He hit out at international observers, including former South African President Thabo Mbeki and former US Secretary of State John Kerry, casting doubt on their credentials.
"Nobody should think this is the end of the matter," he said.
Regional leaders, including Ugandan President Yoweri Museveni and Rwandan President Paul Kagame, have congratulated Mr Kenyatta.
- BBC/ Reuters