One person has died after being shot in overnight protests following the re-election of Kenyan President Uhuru Kenyatta, police said.
Four others were treated for gunshot wounds suffered during the protests in and around Kisumu, a stronghold of defeated opposition leader Raila Odinga. County police commander Titus Yoma confirmed the casualties.
Hundreds gathered early Saturday in the western Kenyan city. They lit bonfires and barricaded streets just hours after the electoral commission announced Kenyatta as the winner.
Violence also broke out in Nairobi's slum of Mathare, where tear gas and gunshots rang out all night, witnesses said.
Most of the protesters were supporters of Odinga, who has rejected the results of the presidential election, calling the vote rigged. National election officials have decried the accusations, saying the vote was free and credible.
Kenyatta, who promised to create 1.3 million jobs, got 54% of the vote to secure a second five-year term; Odinga, who vowed to fight corruption, received 45%.
Most of Kenya is calm
Violence in Kenya could have ripple effects far beyond the nation of 47 million people. As the largest economy in East Africa, Kenya is a crucial trade route to the continent and provides an important buffer of stability in a region that includes the fledgling Somali government and the politically tense Sudan and South Sudan.
Three other people have died since Tuesday's vote, including two killed Wednesday after protests broke out in Nairobi and Kisumu. A polling agent from Odinga's party was killed on Election Day in a machete attack in Tana River county.
Beyond the deadly incident in Kisumu, most of the nation remained relatively calm Saturday.
Amnesty International called on authorities to investigate reports that police shot dead demonstrators in opposition strongholds.
"Everyone has a right to peaceful protest and they must not be hurt, injured or killed for exercising that right," Muthoni Wanyeki, the organization's regional director, said in a statement.
The acting interior minister called reports of protester deaths "lies," saying most of the demonstrators are criminals taking advantage of the chaos.
The incumbent President had appealed for peace after the result was declared Friday.
"Fellow Kenyans, elections come and go but Kenya is here to stay," he tweeted. "Let us always remember that we are all brothers and sisters."
International observers have urged candidates to respect the outcome and resolve any poll disputes through legal avenues.
More than 400 international election monitors -- including from the United States and the European Union -- deployed across the country to monitor voting, the tallying process and the post-election period.
Former US Secretary of State John Kerry, who served as an election observer for the Carter Center, said while there were "little aberrations here and there," the election was not rigged.
"If anything was electronically fiddled with, there is a way to go back and absolutely ascertain what happened in the polling station," he said. "So, by paper ballots, there is a protection of each and every Kenyan's vote."
Extra security forces have been deployed in the capital of Nairobi, interior ministry spokesman Mwenda Njoka said.
Fears of violence
Allegations of vote-rigging have sparked concerns, with some Kenyans fearing ethnic clashes similar to those triggered a decade ago.
Though Kenya's last election in 2013 was mainly peaceful, the country plunged into widespread violence in the aftermath of the 2007 vote.
More than 1,000 people were killed in months of bloodshed following the 2007 election after Odinga -- defeated by then-President Mwai Kibaki -- claimed the vote was rigged.