Navalny's mother Lyudmila was among the mourners, visiting her son's grave for the second day, accompanied by the mother of Alexei's widow Yulia. Both women, dressed in black, stood quietly at the grave, before leaving.

Navalny, who was President Vladimir Putin's fiercest critic inside Russia, died at the age of 47 in an Arctic penal colony on Feb. 16. Supporters said he had been murdered. The Kremlin has denied any state involvement in his death.

Thousands of people attended a farewell ceremony for Navalny on Friday, with some chanting his name and saying they would not forgive the Russian authorities for his death.

By Saturday, the grave in a Moscow cemetery not for from where he once lived was covered with flowers left by thousands of mourners.

"He was the one who had opened my eyes to the existing political situation in Russia," one mourner, who did not give her name, said of Navalny, who rose to prominence with blogs exposing what he said was vast corruption in the Russian elite.

"I followed all of his investigations closely. I showed them to my friends who were not very interested (in politics). I tried to show them to my parents, but that was more difficult. I love truth, I love honesty, and I'm very happy when truth wins."

The Kremlin dismissed Navalny's accusations of corruption and his accusations that Putin had vast personal wealth. Navalny's movement is outlawed and most of his senior allies have fled Russia and now live in Europe.

POLICE LOOK ON

Another mourner visited the grave "to honour the memory of the man who has become a symbol of perseverance for me. And after what's happened, there's a feeling of a very deep sorrow."

"But as horrible as it may sound, it is still pleasant to see how many people came here, and this makes me feel some kind of communion," the mourner said.

"He was a symbol. He was a huge symbol. Despite everything, you can think of him whatever you want, but he has really become a symbol of something free and bright, of some kind of hope."

Police looked on but did not interfere as mourners lay flowers at Navalny's grave on Saturday.

A rights group, OVD-Info, reported that 91 people had been detained on Friday in 12 towns and cities, including Moscow. It did not immediately report any new detentions on Saturday.

Navalny had been jailed on a host of charges including fraud, contempt of court and extremism. He denied all those charges, saying they had been trumped up by the authorities to silence his criticism of Putin.

(Reporting by Reuters, Writing by Maxim Rodionov, Editing by Timothy Heritage)