Kenya's veteran opposition leader Raila Odinga called Monday for weekly protests, as clashes erupted between police and supporters demonstrating over the country's cost-of-living crisis.
"Every Monday there will be a strike, there will be a demonstration," Odinga told crowds of chanting followers in Nairobi. "The war has begun, it will not end until Kenyans get their rights."
Odinga had called Monday's demonstrations against the government of President William Ruto in protest at soaring prices of basic goods in Kenya and what he said was last year's "stolen" election.
The opposition leader narrowly lost his fifth tilt at the presidency in the August poll despite being backed by former president Uhuru Kenyatta.
Riot police had earlier fired tear gas and water cannon on Odinga's motorcade near a Nairobi hotel, where he had been due to hold a press conference before being forced to leave.
Running battles erupted between stone-throwing demonstrators and police in several parts of the capital and at least one other Kenyan city, in the first major unrest since Ruto became president last year.
Millions going hungry
Police used tear gas against protesters gathered at a site near government offices in the heart of Nairobi.
Two dozen people were arrested, including the senate minority leader Stewart Madzayo and one other MP.
Kenyans are struggling as prices for basic necessities soar. The value of the shilling has dropped sharply against the US dollar and a sustained drought has left millions hungry.
In Nairobi's biggest slum Kibera, a bastion of Odinga support, people set tyres ablaze while police used water cannon to disperse protesters.
Demonstrators and police also clashed in the lakeside city of Kisumu in western Kenya, another Odinga stronghold.
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Day of destiny
Nairobi police chief Adamson Bungei said on Sunday that police had received requests to hold two demonstrations late Saturday and early Sunday, when normally three days' notice is required.
"For public safety, neither has been granted," he said.
Interior Minister Kithure Kindiki warned on Sunday that anyone inciting public disorder or disturbing the peace would be prosecuted.
Odinga, the leader of the Azimio la Umoja (Resolution for Unity) party, who described Monday as a "day of destiny," continues to claim that Ruto's August election win was fraudulent and denounces his government as illegitimate.
According to official results, Odinga lost to Ruto by 233,000 votes, one of the slenderest margins in Kenya's history.
The Supreme Court dismissed his appeal against the result, with its judges giving a unanimous ruling in favour of Ruto, finding there was no evidence for Odinga's accusations.
Ruto has declared that he will not be intimidated by the demonstrations, saying: "You are not going to threaten us with ultimatums and chaos and impunity.
"We will not allow that," he said, calling on Odinga to act in a "legal and constitutional manner."
