Police fired tear gas in central Nairobi on Monday to disperse a crowd of several hundred anti-government demonstrators in the streets, a Reuters witness said, as others gathered peacefully for a mass rally called by the opposition at a nearby park.
The demonstrators are opposed to President Uhuru Kenyatta and carried posters of opposition leader Raila Odinga, chanting "Uhuru must go."
Tear gas was also fired in Odinga's home town of Kisumu in western Kenya to disperse a crowd of several hundred angry youth.
In Nairobi, protesters climbed over statues, prompting police to fire half-a-dozen tear gas canisters.
The protesters swiftly dispersed.
Call for dialogue
Odinga, a former prime minister and Kenyatta's main opponent in last year's election, called for Monday's rally to demand dialogue over recent militant assaults, an economic slowdown and other grievances.
He has said it is not a bid to unseat the government.
But the build-up to the rally has stoked tensions in a nation with experience of political violence in the recent past and on edge after a spate of militant attacks, the latest at the weekend when gunmen killed at least 29 people.
"This country is not well and this government hasn't delivered a single thing from their manifesto," said Mohamed Hassan, 30, who was joining the rally in the park in Nairobi. "Raila Odinga wants people to get jobs and [a] poor man to get a good home."
About 2,000 people had gathered by midday in Nairobi, some dancing while music blared and others chanting slogans. The rally is not expected to get underway in earnest until later in the day.
Police chief David Kimaiyo said 15,000 security officers had been deployed on the streets of Nairobi, according to the Associated Press.
He warned demonstrators against marching to the president's official residence, telling a local TV station that it is treasonous to do so.
Kenya's constitution allows picketing.
Odinga is expected to address supporters by 3 p.m. (1200 GMT).
Some businesses in Nairobi have closed for fear of riots, the AP reported.
No to dialogues
Kenyatta aides have dismissed the call for dialogue, saying there are already channels for debate, such as parliament. They have accused the former prime minister of trying to claw his way back to power, a charge Odinga denies.
Tensions were turned up when gunmen attacked two areas on the coast on Saturday, the latest in a series of assaults that have deterred tourists and stoked frustration among Kenyans who say the state is not doing enough to protect them.
Somali Islamist group al-Shabab claimed responsibility for Saturday's attacks - one in Lamu County and the other in Tana County.
But the government suggested local politicians were to blame instead. The opposition have denied any role.
Some information for this report provided by Reuters, AFP and AP.