Thousands of demonstrators gathered in central Moscow during the weekend calling for the release of prisoners jailed since the 2012 "Bolotnaya" riots.

The protesters marched along Moscow streets from Pushkin to Turgenev squares calling for authorities to drop charges against 28 "political prisoners" who were arrested during May 6, 2012, clashes with police in the city over what they called the fraudulent re-election of Russian President Vladimir Putin.

Organizers said the protest drew 12,000 to 15,000 people while the Russian Interior Ministry put the number at 2,000, Interfax reported.

The march, which had been approved by Moscow city authorities, passed without incidents or arrests.

More than 500 people were arrested during the riots in Bolotnaya Square, triggered by the inauguration of Putin to a third term as Russia's president despite allegations of widespread fraud during the election campaign.

Sunday's march was led by liberal politician Boris Nemtsov, an outspoken critic of Putin and founder of the Republican Party of Russia-People's Freedom Party.

Signs carried by protesters included slogans such as "Freedom for the prisoners of May 6" and "Freedom to political prisoners!", while others denounced allegations of corruption in the staging of this week's 2014 Winter Olympic Games in Sochi, Russia, Radio Free Europe/Radio Liberty reported.

The marchers, organized by the Russian Solidarity movement and other opposition groups, chanted the names of Bolotnaya prisoners, including entrepreneur Maxim Lousianin, who was found guilty of using violence against police and sentenced to 4 1/2 years in a penal colony.

Eight of the Bolotnaya prisoners are currently awaiting what could be lengthy sentences of up to six years in prison in connection with the disturbances. It is possible the court hearings on their cases could completed and their sentences announced before the beginning of the Sochi games, the broadcaster reported.

Meanwhile, several of the Bolotnaya defendants have left Russia, such as Anastasia Rybachenko, who is now living in Estonia. Finland in October granted political asylum to defendant Devyatkin Alexei and his wife, Jenny Kurpa, a journalist who took part in the May 6 rally.

Charges against eight others were dropped in December under the presidential amnesty marking the 20th anniversary of the Russian Federation's constitution.

The liberal opposition party Yabloko last week called for the prisoners to be found not guilty.

In an issued statement, Yabloko Chairman Sergei Mitrokhin expressed outrage after public prosecutors demanded lengthy prison terms, declaring such sentences would be "evidence of the repressive character of our judicial and law enforcement systems.

"This punishment is supposed to frighten those who are not afraid of expressing their opinion aloud, attend opposition rallies and dare to protest against the authorities," Mitrokhin said, asserting the cases against them were "demolished by a large number of witnesses.

"There are no video records that prove that the accused took violent actions against the police. The Bolotnaya prisoners became 'guilty without guilt' and are victims of our authorities' repressive policy."