Russian opposition leader Alexei Navalny addresses supporters Saturday at an anti-Putin rally in Moscow.
Moscow CNN  — 

Russian opposition leader Alexei Navalny was detained by police Saturday shortly after arriving at a protest against President Vladimir Putin in Moscow, his official Facebook page said.

Navalny’s team, which organized the protest in Moscow and several other cities in Russia, told CNN he was detained shortly after arriving at central Pushkinskaya Square in the Russian capital.

Images showed Navalny, who was arrested for illegal protest organization, being carried through the crowds by police.

Russian police carry opposition leader Alexei Navalny, center, at an anti-Putin protest Saturday in Moscow.

Putin will be inaugurated Monday as President of Russia for the fourth time, having overwhelmingly won re-election in March.

Navalny, his fiercest opponent, was barred from the race because he carries a fraud conviction, which he dismissed as a politically motivated move to keep him off the ballot.

Protesters chanted “shame” and “Putin is a thief” as they marched through Moscow on Saturday, some carrying placards or Russian flags. When they chanted “we’re fed up,” one elderly man said, “I was fed up 10 years ago.”

Opposition supporters hold placards and shout slogans during Saturday's anti-Putin rally in Moscow.

A police helicopter hovered low over the demonstration to survey the scene. At one point a red smoke flare was set off in the crowd.

A heavy police presence could be seen near Pushkinskaya Square, with riot police and buses standing by. A CNN team saw police officers trying to disperse protesters and escorting them out.

Police said they detained about 300 protesters for public order defenses Saturday, according to Russian state-run news agency TASS.

Those who were detained at the “unauthorized rally” were taken to police precincts for questioning, TASS reported.

Moscow police said about 1,500 people took part in Saturday’s anti-Putin protests to show their outrage over his election win.

A number of pro-Putin supporters also turned up at the protest, their chants drowning out those for Navalny.

Russian authorities demand that applications be filed and the timing and location approved for any rallies, protests or public events.

City officials had not authorized the protest in Pushkinskaya Square. The Navalny campaign had been offered another location away from the city center but went ahead at the unauthorized venue.

Navalny has been arrested many times, including in January, when he led anti-Kremlin rallies in which he called for Russians to boycott the presidential election.

The opposition leader has risen to prominence in recent years by posting investigative stories online about the alleged corrupt practices of Russia’s elite.

Authorities recently shut down his website as well as several social media accounts.

The Kremlin rejects allegations of widespread high-level corruption and condemns Navalny as a dangerous threat to the country’s stability.

CNN’s Emma Burrows reported from Moscow, and Laura Smith-Spark wrote from London.