MOSCOW, December 15 - RAPSI. Whistleblowing lawyer Alexei Navalny, leftist opposition figure Sergei Udaltsov, liberal politician Ilya Yashin and socialite-turned-political activist Ksenia Sobchak were arrested at an unsanctioned rally in Moscow on Saturday.

Activists headed to downtown Lubyanka Square to mark the first anniversary of large-scale opposition protests in Russia by laying flowers at a memorial to victims of political persecution in the Soviet Union.

The rally was not sanctioned by City Hall, giving police the right to detain people in the square.

No mass detentions had taken place as of 15:30 Moscow time, but Udaltsov was detained as he was giving a speech by the memorial; Yashin and Sobchak were stopped as they were approaching the square and Navalny after he gave a speech at the event. The three are reportedly being taken to a nearby police precinct.

The police said that they had been detained for calling people to stage an unsanctioned rally.

A number of other opposition politicians, including Boris Nemtsov and Ilya Ponomaryov, were able to address the crowd by the memorial unhindered by police.

Police said about 500 people showed up, half of them journalists and bloggers, although several media outlets reporting from the scene put the turnout at “several thousand.”

Rallies also took place in several other Russian cities, including Voronezh, Yaroslavl and St. Petersburg, although these had been sanctioned.