Thousands of demonstrators marched through the streets of Moscow in a weekend protest meant to draw attention to those deemed to be political prisoners.

The Sunday march, which began at Pushkin Square in central Moscow and wound through the city's Boulevard Ring to Academician Sakharov Prospect, was peaceful and completed without incidents or arrests, ITAR-Tass reported.

The crowd was estimated by 5,000 by the interior ministry while opposition leader Ilya Yashin said more than 20,000 attended the "March for Freedom," in which demonstrators denounced what they consider a crackdown on political opposition by Russian President Vladimir Putin following his disputed 2012 re-election.

Moscow authorities said some 3,000 police officers and interior ministry troops patrolled the event to "ensure public order and public safety."

The demonstrators called for the release of those held in connection with 2012 Bolotnaya Square protest as well as other "political prisoners."

The Bolotnaya case -- in which 17 young men protesting what they called Putin's fraudulent re-election were arrested May 6, 2012 in Moscow's Bolotnaya Square -- triggered worldwide concerns over the human rights situation in Russia.

Two of the prisoners have been sentenced to 2 1/2 years and 4 1/2 years in jail, one has been committed to psychiatric hospital, 11 are currently on trial and other cases are still being investigated, the Russian broadcaster RT reported.

Putin has stated the demonstrators were justly arrested for advocating mass unrest and calling for violence against police.

"We demand release of prisoners of the Sixth of May. Freedom to political prisoners," a large banner read.

Some called for the release of Greenpeace activists arrested last month while attempting to storm a Russian oil rig in the Barents Sea and for the release of the punk rock band Pussy Riot.

Protesters carried photos of jailed former oligarch Mikhail Khodorkovsky, Pussy Riot's Mary Alekhine and former Yaroslavl mayor Yevgeny Urlashov, an anti-corruption activist whose July arrest on bribery charges is regarded by human rights activists as political intimidation by the Kremlin.

Representatives of Russian liberal and opposition groups such as the Left Front, the RPR-Parnas party, the Russian United Democratic Party Yabloko and the Solidarity movement, as well as environmental and gay-lesbian activists, took part in the march, ITAR-Tass said.

Among those attending the event were former opposition presidential candidate Alexei Navalny, Yabloko leader Sergei Mitrokhin, popular writer Dmitry Bykov and actor Maksim Vitorgan.

Navalny, regarded as Putin's chief political rival, was convicted of theft in July and this month was given a suspended five-year sentence, which will likely rule out another presidential run unless the conviction is overturned on appeal.

He wrote on his Twitter account Sunday it was important to keep up the human rights pressure, Russian broadcaster RBC reported.

"People came out in July and protected me. And we need to protect others," he wrote. "We cannot rely on international public opinion, because international relations are pragmatic."

Putin insists there are no political prisoners in Russia.

During an Oct. 2 economic forum, he dismissed calls for amnesty, saying, "I do not really understand what is meant by political amnesty. We have, in my opinion, no political prisoners."