Police detained Russian opposition leader Alexei Navalny at the entrance of his home on Monday, just before an unsanctioned rally he was going to hold in central Moscow, but the protest will still go ahead, his wife said on Twitter.
Electricity in Navalny's office was switched off, his spokeswoman said in a separate Twitter message. A live Internet feed run from Navalny's office went off air.
News of his arrest followed protests by thousands of his supporters with reports of several being arrested as police warned organisers against holding an unauthorised rally in Moscow.
The Reuters news agency reported that more than 100 people were arrested in Moscow, while according to the NGO OVD-Info 121 people were arrested in Moscow and a further 137 were arrested in St Petersburg.
OVD-Info further reported that 25 people were detained in Sochi and another 10 each in Vladivostok and Norilsk.
The protest is the second mass action since March 26 called by Navalny, who has announced his intention to run for president next year and has drawn a new generation to the streets through a relentless online campaign.
The 41-year-old's anti-corruption videos have needled the country's most powerful and drawn a new generation into politics.
Novosibirsk and more
Local media said roughly 3,000 people protested in the Siberian city of Novosibirsk. Smaller rallies also gathered in Krasnoyarsk, Kazan, Tomsk, Vladivostok and many other cities.
Russian website OVD Info, which operates a hotline and tracks detentions at protest events, said about 10 people were detained ahead of the start of the rally in Moscow at 2pm (1200 GMT).
On the eve of the event, Navalny announced he was moving the the venue of the Moscow demonstration because the City Hall had blocked organisers' efforts to obtain a stage and sound equipment at the designated location.
Authorities "are forbidding any contractors from getting us a stage and sound," he wrote on his blog Saturday evening.
"We are cancelling the rally on Sakharov Avenue and moving it to Tverskaya Street," a main thoroughfare to the Kremlin, he said.
Moscow City Hall labelled the decision a "provocation" while the police warned that a different event was being held at Tverskaya and that the protest would clash with festivities.
Russia on Monday marks a holiday called Russia Day with President Vladimir Putin expected to issue awards and hold a reception in the Kremlin.
Various events are held around Moscow, including the reconstruction of scenes from various eras of Russian history.
"Any provocative actions by the protesters will be viewed as threat to public order and immediately thwarted," the police said.
The mood was tense ahead of the rally as some groups of protesters vowed to go to the authorised location.
The protest on March 26 was the biggest anti-Kremlin event in years and saw hundreds of people detained in the capital, including Navalny himself who spent 15 days in jail.
Navalny called the anti-corruption protests after releasing a film alleging that Prime Minister Dmitry Medvedev controls a vast fortune through a network of foundations.
The video has been viewed on YouTube over 22 million times.