Police have roughly detained more than 100 activists at anti-government rallies in Moscow and St. Petersburg.
The gatherings on Sunday evening were the latest in a series of protests that opposition leaders call on the last day of every month with 31 days, with the date a reference to the 31st Article of the Constitution, which guarantees freedom of assembly.
This month, however, the activists in Moscow adopted a new tactic and about 100 of them sat down near Triumfalnaya Ploshchad in what appeared to be an attempt to demonstrate that their protest would be peaceful.
Moscow police, who usually break up the opposition protests, which are often unsanctioned by city authorities, also appeared to have taken a new approach. The police said they would not detain the activists Sunday as long as they posed no danger to pedestrians.
After two hours, however, the activists stood up and began to march toward the Kremlin. Police moved in quickly and detained dozens.
Police said 43 people were detained, but Alexander Averin, a member of The Other Russia opposition party, put the figure at 67 people, Interfax reported Monday. He said two activists, Sergei Udaltsov and Konstantin Kosyakin, remained in detention Monday, charged with disobeying police orders.
In St. Petersburg, police said about 50 protesters were detained.