A Moscow court on Monday sentenced a 23-year-old actor to three-and-a-half years in prison for violence against police at an opposition protest even though he claimed he was simply a bystander.

Moscow's Tverskoy district court sentenced actor Pavel Ustinov to serve the sentence in a penal colony despite pleas from activists and prominent figures to let him go.

Ustinov denied any guilt, insisting he was a passerby and was not taking part in the protest.

Investigators said Ustinov violated public order during an unauthorised rally on August 3 and put up resistance during his arrest. As a result, a policeman sprained his shoulder.

Footage from the scene showed several police in full riot gear lunging at Ustinov -- who was standing with a phone in his hand near a metro station -- and beating him with batons.

Prosecutors had asked the court to sentence him to six years in prison.

President Vladimir Putin's spokesman Dmitry Peskov said the Kremlin did not comment on court rulings.

The latest sentencing brought to six the number of people jailed for taking part in a recent wave of anti-government demonstrations.

Tens of thousands of people took to the streets of Moscow after authorities refused to allow prominent opposition candidates to stand for the city parliament in September 8 elections.

Police detained hundreds of the protesters, and while most were quickly released, some faced serious charges.

In the week ahead of the elections, five were sentenced to jail time ranging from two to four years.

On top of that, a blogger was sentenced to five years in a penal colony for a tweet calling for attacks on the children of police. The tweet came in response to the crackdown on the protesters.

While some of the jailed people were opposition activists, others like Ustinov were merely bystanders who got caught up in the authorities' crackdown on dissenters, observers say.

- 'Crime of the authorities' -

This month Danila Beglets, a father of two and the sole breadwinner of his family, was sentenced to two years in prison for attacking a policeman.

At first he insisted he did not take part in the rally but later admitted guilt under apparent pressure from investigators.

In a video address ahead of the ruling, renowned Russian film and theatre actor and director Konstantin Raikin said he knew Ustinov well and was sure he was not guilty.

‘This is a mistake which may end in tragedy,’ he said, calling on the authorities not to ‘ruin his life’.

Political analyst Alexander Morozov said on Facebook the case against Ustinov was a ‘crime committed by the authorities, by the entire law enforcement system.’

Protesters said their rallies were peaceful, while rights groups and Western countries have accused Russian police of using excessive force against demonstrators.

The protests and ensuing crackdown were the biggest since a wave of demonstrations in 2011-12 against Putin's return to the Kremlin.