MOSCOW — Police in Moscow detained Russian opposition leader Alexei Navalny for most of the day Friday in an apparent bid to prevent him from joining a rally that he organized in another city, where several people were also detained.

Navalny had planned to travel to the Volga River city of Nizhny Novgorod where he was to lead a rally, the latest in a series of demonstrations he has organized across Russia, when he was detained early Friday. He was kept at a Moscow police station until late evening.

After he announced his presidential bid last year, Navalny, a top Kremlin foe and arguably Russia’s most popular opposition politician, inspired a grassroots campaign in Russian regions to support his nomination. The crackdown comes after he held rallies in six Russian cities, from Murmansk in the northwest to Khabarovsk on the border with China.

Navalny posted a video on his Instagram account early Friday of what he said were officers outside his home asking him to come to a police station. He said he was held there without charges or any explanation why he had been detained.

The Interior Ministry said in a statement Friday that Navalny was detained because of his calls for unsanctioned rallies.

The rally in Nizhny Novgorod, however, had received City Hall approval. When several hundred people gathered for the rally Friday evening, police ordered them to disperse and detained several demonstrators.

After his release, Navalny tweeted that the authorities’ efforts to derail opposition rallies will fail.

“A plan to block regional rallies won’t work,” Navalny said, adding that other demonstrations are set to be held in Orenburg in the Urals and Arkhangelsk in northwest.

Navalny has been summoned to attend a court hearing Monday on charges of violating the rules of organizing a rally.

His campaign chief, Leonid Volkov, was kept in police custody in Nizhny Novgorod for most of the day Friday until being released and ordered to attend Monday’s court hearing on the same charges.

“The Kremlin views my meetings with voters as a huge threat and even an insult,” Navalny tweeted. “They were saying for so long that opposition has no support in the regions, and it now pains them to even look at our rallies.”

The Kremlin has dismissed Navalny, who has faced repeated jailings and criminal cases, as an urbanite out of touch with people living in Russia’s 11 time zones where President Vladimir Putin draws his support from.

That began to change earlier this year when Navalny opened campaign offices in 80 cities and towns, most of which had not seen a political life for decades, attracting thousands of supporters.

In Germany, Ulrike Demmer, a spokeswoman for Chancellor Angela Merkel, told reporters Friday that the German government “views the arrests of activists including Navalny … with incomprehension and great concern.”

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Vladimir Isachenkov in Moscow and Geir Moulson in Berlin contributed to this report.