Updated

Jailed Russian opposition activist Ildar Dadin says he has been tortured by prison guards.

Dadin said he was beaten and hung up with handcuffs at a prison in northern Russia, according to a letter sent to his wife and released Tuesday to Russian media.

Prison officials told the Novaya Gazeta newspaper that physical force had been used against Dadin, but said it took place only when he refused to leave his cell. Dmitry Peskov, spokesman for President Vladimir Putin, the incident should be investigated by relevant authorities.

Dadin, currently serving a 2½ year sentence, was the first person to be jailed under strict new laws passed in 2014 regulating public demonstrations.