Violence erupted during opposition protests which raged overnight into Saturday after the controversial election victory of President Uhuru Kenyatta.
At least 11 people were killed on Saturday in protests that erupted in Kenya's western city of Kisumu following the re-election of President Uhuru Kenyatta.
In Nairobi, a young girl was shot dead by police firing "sporadic shots" at protesters in Mathare, a witness said.
The run-down neighbourhood is loyal to opposition leader Raila Odinga, whose party has rejected the results of Tuesday's vote as a "charade".
A government official told reporters another man was killed in Kisumu county, centre of serious post-election ethnic violence in 2007 in which 1,200 people were killed and 600,000 displaced.
Kisumu's main hospital was treating four people brought in overnight with gun-shot wounds and six who had been beaten by police, hospital records showed.
More shooting was heard outside the hospital on Saturday morning. In Nairobi, Kenyan television showed footage of armed police units backed by water cannon moving through the rubble-strewn streets of Kibera, another pro-Odinga Nairobi slum.
The election commission announced its official results late on Friday, giving 55-year-old Kenyatta another five years in power after securing 54.3 percent of votes cast.
Odinga's NASA coalition rejected the results even before they were announced, saying that the election commission's systems had been hacked.
Kenya's main monitoring group backed the official result of this week's ballot