Kenya's President Uhuru Kenyatta has been re-elected following Tuesday's election, officials say.
Mr Kenyatta, in office since 2013, took 54.3% of votes, ahead of his rival Raila Odinga, with 44.7%.
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 have 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.
Police, who were deployed in anticipation of the results, have fired tear gas in several locations.
Fires have been lit by protesters on a road in the heart of Kisumu, a BBC reporter at the scene says. Gunshots have also been heard.
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 1,100 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".
Vote settles old rivalry - by Dickens Olewe. BBC News
Raila Odinga has come up short again in what was his fourth and probably last attempt to become the president of Kenya.
Polls had shown that he was tied with President Kenyatta in a race tipped to go either way. Well, they were wrong. An opposition alliance's backing for Mr Odinga was not enough to stop Mr Kenyatta's re-election.
The 72-year-old opposition leader had campaigned as a change candidate, calling himself the biblical Joshua and promising to lead Kenyans to Canaan, the promised land.
Despite the fact that he rallied and excited thousands across the country, a majority of voters have rejected his message, or rather rejected him, and embraced Mr Kenyatta's vision of transforming the country.
This election was also about the political duel between the Kenyatta and Odinga families, which dates back to Kenyan independence in 1963. Once again, the Kenyatta camp has won.
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.