It has been the largest wave of arrests at political events in Russia since September 2022, when more than 1300 were arrested at demonstrations against a "partial mobilisation" of reservists for Putin's military campaign in Ukraine.
Navalny, a 47-year-old former lawyer, fell unconscious and died on Friday after a walk at the "Polar Wolf" Arctic penal colony where he was serving a three-decade sentence, the prison service said.
OVD-Info, which reports on freedom of assembly in Russia, said the largest numbers of arrests occurred in St Petersburg and Moscow, where Navalny's support had traditionally been strong. As of 20:00 GMT on Saturday, more than 200 people were detained in St Petersburg.
But there was no mention of the events on Russian state news agencies, which are under full Kremlin control. There was also no stories about the hundreds of people across Russia who have continued to defy authorities to lay flowers at impromptu Navalny memorials.
The death of Navalny robs the disparate Russian opposition of its most prominent leader as Putin prepares for the March presidential election - a rubber-stamp vote set to keep the former KGB spy in power until at least 2030.
Footage filmed by Reuters on Saturday in St Petersburg showed dozens gathering by a monument to the victims of repression. Protesters laid flowers and candles, while some sang hymns and others hugged each other, shedding tears.
"I felt very sorry for him and for our country," said an 83-year-old woman attending the vigil who declined to give her name. "I'm scared."
A Reuters reporter at the scene said some 30 people were arrested shortly after the singing finished.
FLOWERS KEEP APPEARING
OVD-Info also reported individual arrests in smaller cities across Russia, from the border city of Belgorod, where seven were killed in a Ukrainian missile strike on Thursday, to Vorkuta, an Arctic mining outpost once a centre of the Stalin-era gulag labour camps.
The online news outlet SOTA reported that in Luhansk, an Ukrainian territory now under Russian control, residents laid flowers in Navalny's honour at a monument commemorating the victims of the Soviet Union leader Joseph Stalin.
In another city, flowers were laid at a monument to the heroes of the early 20th century Russian Revolution.
"Despite the authorities' attempts to remove the flowers, they keep appearing," SOTA reported.
Footage filmed by Reuters in Moscow showed law enforcement bundling people to the ground in the snow, close to a spot where mourners had left flowers and messages in support of the dead opposition leader.
"In each police department there may be more detainees than in the published lists," OVD-Info said. "We publish only the names of those people about whom we have reliable knowledge and whose names we can publish."
Reuters could not immediately verify the count. Police declined to comment.
