Supporters of the late Russian opposition leader Alexei Navalny have visited his grave in Moscow to mark one year since he died in an Arctic penal colony.

President Vladimir Putin's administration has been tightening crackdowns on dissent and curtailing freedom of speech after the death of Navalny.

People believed to be linked to the interior ministry were keeping watch on mourners at the cemetery on Sunday.

A Navalny supporter said people in Russia unfortunately live in a reality where freedom of speech, or freedom of anything, sounds like a fairy tale.

Another supporter said Navalny gave people hope and faith that everything will eventually turn out well.

Russian authorities revealed Navalny's death on February 16 last year. They said he had died of natural causes.

But his widow, Yulia Navalnaya, accused the authorities of playing their hand in fatally poisoning him. An article carried by a Russian independent investigative reporting website last September also said official documents it had obtained confirmed he was poisoned in prison.