A Russian opposition activist jailed for assaulting police during a protest in Moscow has been handed an additional two years in jail.

Sergei Mokhnatkin was found guilty of "disrupting operations of a penitentiary" on March 20 and sentenced the same day, activist Tatyana Pashkevich wrote on her Facebook account.

The Arkhangelsk regional prosecutor's office told Interfax that Mokhnatkin's remaining time in a maximum-security penal colony will end 2 1/2 years from March 20.

Mokhnatkin was sentenced to 4 1/2 years in prison in 2014 after being found guilty of assaulting two police officers during a December 2013 protest in Moscow.

Mokhnatkin's lawyers say he was severely beaten by penal-colony guards in March 2016 after he refused to be transferred to a detention center without a written ruling. He was then charged with insulting a guard and disruption of the penal colony's operations.

In June, Mokhnatkin was found guilty of insulting a guard and sentenced to an additional 11 months. That prison time runs concurrently with his March 20 sentence.

Mokhnatkin first came to prominence in 2009 when he was sentenced to 2 1/2 years in prison after being convicted of attacking a police officer during another opposition rally. He was pardoned by then-President Dmitry Medvedev in April 2012.