Six people have been killed in clashes between police and demonstrators who joined a banned opposition protest against a new finance law, police officers told AFP news agency.
Police had earlier on Wednesday fired tear gas on protesters in and around Nairobi, with five of the six deaths reported in the towns of Mlolongo and Kitengela on the capital's outskirts.
Tear gas was also used to disperse crowds attacking a highway connecting Nairobi to the port city of Mombasa, with one death recorded in Emali, a town located along that route.
"We have three deaths in Mlolongo, where a group of demonstrators had blocked the road to protest, and we also have two others in Kitengela and one in Emali," a police officer said.
"There was a confrontation with police officers deployed to quell the riots and some (people)... were shot in the process," he said on condition of anonymity.
A second policeman said, "I can confirm the deaths in Mlolongo, Emali and Kitengela," without elaborating further.
'Bullets and tear gas'
Opposition leader Raila Odinga, pursuing a protest campaign against the government, had urged demonstrations against a finance law that has seen fuel prices surge, adding to the difficulties faced by poor Kenyans.
But late on Tuesday, police chief Japhet Koome said the authorities had not received any official notification of rallies, as required by law.
"All lawful means will be used to disperse such demonstrations," he warned.
Odinga and opposition politicians accused police of being heavy-handed.
"We have always said that these meetings remain peaceful until police decide to break them up with bullets and tear gas," Odinga said. "Police have shot, injured and killed protesters in various parts of the country including here in Nairobi."
But he said he was calling off plans to address supporters in the capital, citing fears for their safety.
Kenyan police have also been criticised by human rights watchdogs for their response to protests.
Fifty-three children were treated after tear gas was thrown into their school, a health records worker at the Eagle Nursing Home clinic in Nairobi's Kangemi neighbourhood told the Associated Press.
The children aged 10 to about 15 had been in shock, said Alvin Sikuku. “At this point they are OK, with their parents,” he said Wednesday evening, and tensions around the incident were fading: “Right now, things are cool.”
One civil society watchdog, the Independent Medico-Legal Unit, said in a statement it was “horrifying to hear about police officers using such excessive force.”