An AFP correspondent saw a mixture of plainclothes police wearing black and officers in uniform detain at least 30 protesters, some of whom were elderly, and place them in police vans in the former capital Almaty as they gathered for a planned demonstration.
The rare opposition protest ostensibly backing educational reforms was called for on social media by Mukhtar Ablyazov, an exiled oligarch who is 77-year-old Nazarbayev's most significant political opponent.
Nazarbayev has ruled Kazakhstan for nearly three decades, tolerating almost no opposition at home. A court in the country ruled that Ablyazov's Democratic Choice of Kazakhstan movement was an extremist group earlier this year.
The attempts to hold opposition protests come at a sensitive time in the oil-rich Central Asian country amid mounting speculation that Nazarbayev will not stand again when his present presidential term ends in 2020.
'Up to 50' detained
The head of the Almaty-based Kazakhstan International Bureau for Human Rights monitor Yevgeny Zhovtis told AFP that "the majority of the detained have now been released" without charge.
"But some are still at police stations," he said, noting that one of his colleagues at the rights group was among those detained and then released.
Zhovtis put the overall number of detained in Almaty at "up to 50."
An AFP correspondent in the capital Astana could not confirm media reports of detentions at a similar protest planned there.
The state prosecutor's office and the ministry of internal affairs declined to comment on the detentions when contacted by AFP.
A journalist in the northwestern city of Uralsk told AFP that four of his colleagues from the city's leading independent newspaper Uralsk Week and a reporter from Radio Free Europe were detained while intending to cover a rally that did not take place.
Uralsk Week journalist Raul Uporov told AFP the journalists were formally taken to a police station for questioning as witnesses over an unrelated case.
The Radio Free Europe journalist was later released as well as three journalists from the newspaper.
Political rallies are deemed illegal unless officially sanctioned in Kazakhstan, a law that rights groups say is designed to suppress civil society.
Ablyazov, who is believed to be based in France was last year found guilty of embezzling billions of dollars from BTA bank, once a leading lender in the republic, in an investigation dating back to 2009, when he fled the country.
He received a 20-year sentence in absentia and has denied any wrongdoing.
He promised to topple the Kazakh government "in the space of three years" after France refused to extradite him to Russia in December to face separate charges of corruption linked to BTA in 2016.
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