Russian security services said on Sunday they had detained 263 people in the center of Moscow for "breach of public order".
It was the latest announcement of a sweep of potential anti-government protesters around this weekend's marking of Unity Day, essentially the successor to Soviet celebrations of the October 1917 coup that brought the Bolsheviks to power.
Reuters reporters said they had seen police detain a few dozen on a Moscow street, although none of those detained had any posters, nor were they chants slogans.
The FSB, the successor to the Soviet-era KGB, said on its web site on Friday that it had arrested all the members of Artpodgotovka, an anti-government movement in the Moscow region, and seized 15 bottles of Molotov cocktail.
It said the group had planned "extremists actions in the form of arson of administrative buildings with the use of incendiary fuel and attacks on the members of police to provoke mass unrest" on Nov. 4-5, Unity Day weekend.