Russian opposition leader Alexei Navalny was arrested on Monday shortly before he headed to central Moscow to attend a protest.
His wife announced on Twitter that Navalny was detained at the entrance of his home in the Russia capital. She added that the unsanctioned protests will go ahead.
The protests kicked off shortly afterwards.
Police in riot gear started detaining anti-Kremlin protesters in central Pushkin Square, while using loud hailers to tell them to disperse, Reuters witnesses said.
Around 1,000 protesters started to move from the square towards the Kremlin, but their path was blocked by police barriers put in place as part of a festival of historical costumes on Tverskaya Street, Moscow’s central thoroughfare.
A Reuters journalist at the scene saw about 15 people detained by police.
Navalny scheduled the protests against what he says is a corrupt system of rule overseen by Russian President Vladimir Putin.
The scale of the protests will show if Navalny, who is mounting a long-shot bit to unseat Putin in a presidential election next year, can build on the success of a similar event in March, in which thousands took to the streets across Russia.
Those protests were the largest since a wave of anti-Kremlin demonstrations in 2012 and resulted in over 1,000 arrests, putting rare domestic pressure on Putin, who is expected to run for and win re-election next year.
Monday is Russia Day, a public holiday, a factor that may boost turnout.
Authorities in Moscow, where the largest protest is likely to be held, authorized a venue away from the center.
But Navalny said late on Sunday that the authorities had pressured firms into refusing to supply him and his allies with sound and video equipment, a move he said was designed to humiliate protesters.
For that reason, he said he was unilaterally switching the venue to Tverskaya Street, near the Kremlin. The General Prosecutor’s Office warned that a protest there would be illegal and police would be forced to take “all necessary measures” to prevent disorder.
A legal “caution” was being readied for Navalny, it said. Kremlin spokesman Dmitry Peskov told TV Rain it was vital to avoid what he called “provocations.”
The protest threatened a festival planned for Tverskaya which has already been turned into a pedestrian zone by actors re-enacting periods of Russian history with props such as World War Two jeeps and artillery guns.
Reuters reporters saw a heavy advance police presence on and around the avenue with bus loads of riot police parked nearby, side roads blocked, and airport-style metal detectors installed at pinch points.
For now, polls suggest Navalny has scant chance of unseating Putin, who enjoys high ratings. It is unclear too if the Kremlin will even let Navalny run for the presidency.
But the 41-year-old lawyer turned political street campaigner hopes anger over corruption may boost his support.
A video he made accusing Prime Minister Dmitry Medvedev, a Putin ally, of living far beyond his means has garnered over 22 million online views to date.
Medvedev said Navalny’s allegations were politically motivated “nonsense” and called him a charlatan.
Navalny, who had a green liquid thrown in his face in April, robbing him of some of his sight, said hundreds of people had attended demonstrations in Russia’s Far East on Monday morning.
The Moscow protest is due to run from 1100 to 1400 GMT.
“I want changes,” wrote Navalny in a blog post last week. “I want to live in a modern democratic state and I want our taxes to be converted into roads, schools and hospitals, not into yachts, palaces and vineyards.”
The Kremlin has long sought to cast the opposition as a phenomenon of a privileged, Westernized urban elite out of touch with people in Russia’s far-flung regions.
Monday’s protests could demonstrate that the opposition has significant support throughout the vast country.
Navalny’s website reported Monday that protests were held in more than a half-dozen cities in the Far East, including the major Pacific ports of Vladivostok and Khabarovsk and in Siberia’s Barnaul. Photos on the website suggested turnouts of hundreds at the rallies.
Eleven demonstrators were arrested in Vladivostok, according to OVD-Info, a website that monitors political repressions.
Navalny has become the most prominent figure in an opposition that has been troubled by factional disputes. He focuses on corruption issues and has attracted a wide following through savvy use of internet video.
Navalny has announced his candidacy for the presidential election in 2018. He was jailed for 15 days after the March protests. In April, he suffered damage to one eye after an attacker doused his face with a green antiseptic liquid.