Vladimir Putin the Russian opposition and by international observers from the Organization for Security and Co-operation in Europe for procedural irregularities. Anti-Putin protests took place during and directly after the presidential campaign. The most notorious protest was the Pussy Riot performance on 21 February, and subsequent trial. An estimated 8,000–20,000 protesters gathered in Moscow on 6 May, when eighty people were injured in confrontations with police, and 450 were arrested, with another 120 arrests taking place the following day. A counter-protest of Putin supporters occurred which culminated in a gathering of an estimated 130,000 supporters at the Luzhniki Stadium, Russia's largest stadium.
Camps for Russian prisoners and internees in Poland (1919–24) were also exchanged among two sides. Ekaterina Peshkova, the chairwoman of organization "Assistance to Political Prisoners" (Pompolit, "Помощь политическим заключенным", Помполит), was awarded an order of Polish Red Cross for her participation in the exchange of POWs after the Polish-Soviet War. During the memorial ceremony for the victims of the Katyn massacre on April 7, 2010, attended by the Russian and Polish Prime Ministers Vladimir Putin and Donald Tusk, Putin said that, in his private opinion, Stalin (whose refusal to obey orders from the Kremlin resulted in the Russian defeat against Poland in 1920) felt personally responsible for this tragedy,