Police warned organisers against holding an unauthorised rally in Moscow

Russian opposition politician Alexei Navalny was detained in Moscow on Monday as he headed to a protest in Moscow, as thousands of his supporters rallied across the country.

The demonstration is the second mass action since March 26 called by Mr. 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.

"Alexei has been detained in the stairwell," his wife Yulia wrote on his Twitter account about 40 minutes before the anti-corruption rally called by the Kremlin critic was set to start in the city centre.

She posted a photo of him getting into a police car in the street outside their home.

Mr. Navalny supporters were demonstrating across Russia, with several arrested as police warned organisers against holding an unauthorised rally in Moscow.

The 41-year-old's anti-corruption videos have needled the country's most powerful and drawn to the streets crowds unseen since a wave of protests against President Vladimir Putin's re-election to a third term in 2012.

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.

Mr. Navalny's team have been broadcasting about the various actions from a studio set up in Moscow, but it went off air just as Mr. Navalny was being picked up by police.

"They turned off the electricity in the studio," said presenter Leonid Volkov in complete darkness shortly before the channel went off air, to come back online after a few minutes.

Russian website OVD Info, which operates a hotline and tracks detentions at protest events, said 27 people were detained in other cities before the Moscow protest was set to begin at 2 p.m. (1100GMT).

'We support Navalny'

The wave of protests called by Mr. Navalny coincides with public holiday, Russia day, with Mr. Putin handing out awards and holding a reception in the Kremlin.

On the eve of the event, which authorities had authorised in central Moscow, Mr. Navalny announced the protest was changing location after authorities blocked his efforts set up a stage and sound equipment.

Authorities "are forbidding any contractors from getting us a stage and sound," he wrote on his blog on Sunday.

"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.

"Any provocative actions by the protesters will be viewed as threat to public order and immediately thwarted," the police said.

To mark Russia Day, the City Hall closed off Tverskaya Street to road traffic and set up a chain of events like re-enactment of various eras in Russian history, from World War I trenches to a Rennaissance fair and sword-fighting.

In surreal scenes, dozens of civilian buses filled by policemen were parked nearby ahead of the unsanctioned rally while ordinary people gawked at actors in period costumes.

The mood was tense as some groups of protesters vowed to go to the authorised location and worried doing otherwise could get them arrested.

Some protesters however heeded his call to change locations. "We support Navalny," said 16-year-old Yegor with a poster saying "Corruption steals the future."

"We want the turnover of power, like in ordinary countries," he said.

The protest on March 26 was the biggest anti-Kremlin event in years and saw hundreds of people detained in the capital, including Mr. Navalny himself who subsequently spent 15 days in jail.

Mr. Navalny called the anti-corruption protests after releasing a film alleging that Russian Prime Minister Dmitry Medvedev controls a vast fortune through a network of foundations.

The video has been viewed on YouTube over 22 million times.