Russian police detained more than 60 activists in Moscow and St Petersburg on Tuesday at demonstrations against restrictions on freedom of assembly, according to Reuters. Opposition activists stage demonstrations on Triumph Square in central Moscow and Nevsky Prospekt in St Petersburg on the last day of each month with 31 days -- symbolising the right to free assembly secured under Article 31 of Russia's constitution. Russia holds presidential elections next year, when both President Dmitry Medvedev and his mentor Prime Minister Vladimir Putin could run. In St Petersburg, Russia's second biggest city, at least 300 protesters gathered in Nevsky Prospekt. Police detained some and dragged them to police buses, a Reuters reporter said. Interfax corporate news agency quoted a police source as saying 40 had been detained. "Russia will be free" and "Free elections" were among the posters held by protesters. Local opposition leader Olga Kurnosova was among the activists detained in St Petersburg. "The lower the ratings of (Putin's) United Russia party fall, the more toughly we are dispersed," she told Reuters by telephone from a police station. "We can't just keep silent. It is not about a violation of the constitution, it's about common sense." Russia will hold parliamentary elections in December. Recent polls show the United Russia party's approval ratings have been falling . A helicopter hovered over the crowd in St Petersburg, a tactic used police during similar protests in March in an apparent attempt to intimidate demonstrators. In Moscow, police officers and journalists outnumbered several dozen protesters who gathered on Triumph Square, some holding posters and shouting slogans. Twenty six protesters, including opposition leaders Eduard Limonov and Ilya Yashin, were detained in Moscow, Interfax reported. Protesters said at least 50 people were detained.