Kenyan police have killed at least 11 people in a crackdown on protests, as anger over the re-election of President Uhuru Kenyatta erupted, officials have said.
However, the NASA opposition coalition, led by four-time presidential hopeful Raila Odinga, put the death toll at more than 100, including 10 children, but did not provide evidence.
Mr Odinga has rejected the poll and its result as "massive" fraud.
The eruption of violence has revived memories of a decade ago, when Mr Odinga, now 72, lost an election in controversial circumstances that sparked a wave of political and ethnic unrest in which 1,200 people were killed and 600,000 displaced.
Kofi Annan, the former UN head who mediated during that crisis, earlier issued a statement warning Kenya's leaders to "be careful with their rhetoric and actions in this tense atmosphere".
Governments denies accusations of police brutality
The Kenya National Commission on Human Rights said 24 people had been shot dead by police since Tuesday, election day.
Top Odinga lieutenant Johnson Muthama said police had been packing corpses into body bags and dumping them, remarks likely to exacerbate the tensions that followed the official announcement that Mr Kenyatta had won, with 54.3 per cent of votes.
Mwenda Njeka, a spokesman for the Interior Ministry, said the opposition claims were "hogwash".
Acting Interior Minister Fred Matiang'i had earlier said trouble was localised and blamed it on "criminal elements" rather than legitimate political protest.
He also denied accusations of police brutality.
"Let us be honest — there are no demonstrations happening," he said.
"Individuals or gangs that are looting shops, that want to endanger lives, that are breaking into people's businesses, those are not demonstrators.
"They are criminals and we expect police to deal with criminals how criminals should be dealt with."