The United States warned Kenya's rival political camps to reject violence and respect electoral law on Friday, as protesters took to the streets.
Kenya is due to vote on October 26 in a re-run of an August presidential election that was marred by widespread irregularities, and tensions are mounting.
Opposition leader Raila Odinga has called for protests to force President Uhuru Kenyatta's government to overhaul the east African nation's electoral commission.
The majority Jubilee Party has rejected this demand and, amid threats of boycotts, observers are worried about a possible outbreak of political violence.
"The United States Government is deeply concerned by the deterioration in the political environment in Kenya," State Department spokeswoman Heather Nauert said.
"Unfortunately, in recent weeks actors on all sides have undermined the electoral commission and stoked tensions," she said.
"While we support freedom of speech, baseless attacks and unreasonable demands on the electoral commission are divisive," she said, in a rebuke to Odinga's campaign.
But she also warned against overreaction by the security forces.
"Kenyan leaders and citizens must reject violence and call on others to do the same," she said.
"Security services should use the utmost restraint in handling demonstrations, and any response must be proportionate and appropriate."
Meanwhile, police fired teargas to disperse protests Friday as opposition supporters took to the streets in three main Kenyan cities.
© 2017 AFP