MOSCOW (AP) — Several thousand protesters marched through central Moscow on Sunday to call for the release of 20 people who were arrested after clashes between police and demonstrators in May 2012.

Some of them face up to 10 years in prison if convicted for the protest, held on Bolotnaya Square on the eve of President Vladimir Putin's inauguration to a third term as Russia's president.

Putin's return to the presidency saw the passing of new laws aimed at cracking down on anti-government protests and restricting non-governmental organizations.

The protesters marched Sunday with portraits of the jailed protesters and a banner stretching across the street reading: "Freedom to the Bolotnaya heroes, the hostages of Putin."

Some also carried Ukrainian flags to show their support for the anti-government protesters in neighboring Ukraine, where demonstrations have been going on for more than two months.

Of the 28 people rounded up in the Bolotnaya case, eight were recently freed on amnesty. Several defendants have been under house arrest, but most of the others have been in jail for more than a year and a half.

Only three of the cases have been decided: Two defendants received light sentences after cooperating with investigators and a third was sent for forced psychiatric treatment. That man, Mikhail Kosenko, who was convicted of beating a policeman, had a history of schizophrenia, but rights activists charged the court was reviving the Soviet-era practice of using punitive psychiatry against dissidents.