Riot police fired teargas at hundreds of supporters of opposition challenger Raila Odinga and his Orange Democratic Movement (ODM) coalition, blocking a road near Nairobi's Mathare slum, witnesses said.
Reuters photographer Antony Njuguna said about 40 police officers were facing off with hundreds of demonstrators near Mathare, one of the flashpoints during nearly three weeks of violence that has convulsed the east African nation.
"There's a massive crowd trying to block the road. Police are shooting teargas at them," he said from the scene.
In the western opposition stronghold of Kisumu, riot police shot in the air and struck at least one man as they battled youths who set up blazing roadblocks and gathered to protest.
"My father was shot as he stood in front of our house. The police were shooting indiscriminately, targeting anyone on sight. My father was shot in the stomach," witness Alphonse Otieno said by phone from Kisumu's Kondele slum.
Kisumu saw the worst violence on Wednesday, the first of three days of nationwide demonstrations called by the opposition.
Police have banned the rallies called by Odinga, who says Kibaki stole the December 27 election. The government in turn accuses his side of rigging votes and of protesting instead of using legal options to challenge the result.
Kenya's sudden descent into crisis has tarnished its democratic credentials, horrified world powers, scared off tourists and hurt one of Africa's most promising economies.
Police have met the latest unrest with tear gas and live ammunition as they did in earlier protests which ground the east African nation to a halt, delaying school openings and shutting businesses.
On Wednesday, police shot dead three in Kisumu - which erupted in a spree of looting and rioting immediately after Kibaki was sworn in on December 30.
ODM spokesman Salim Lone condemned one killing, captured on television, as a "cold-blooded execution."
In footage shown by local broadcaster KTN, a Kisumu policeman was seen firing his assault rifle at a young man who fell down, and then was kicked by the officer.
