Russia’s prison service said Navalny died after a walk in his Arctic prison on Friday.

His mother, Lyudmila Navalnaya, travelled to the remote colony on Saturday but has still not been allowed access to her son’s body.

“Alexei’s mother and his lawyers arrived at the morgue early in the morning. They were not allowed to go in. One of the lawyers was literally pushed out. When the staff was asked if Alexei’s body was there, they did not answer,” Navalny’s spokesman Kira Yarmysh said on social media.

The charismatic Navalny was President Vladimir Putin’s main political opponent.

His death came three years into his imprisonment in Russia.

He died in the Russian Far North in one of Russia’s harshest prisons after his health had deteriorated for months.

Putin has not yet commented on the death.