Moscow, Russia (CNN) -- Two opposition leaders and a human rights activist were detained in Russia on Sunday after taking part in rallies marking the country's National Flag Day, the Interfax news agency reported.
Those detained were identified by Interfax as Solidarity opposition leaders Boris Nemtsov, a former deputy prime minister, and Mikhail Shneider; and the leader of the Movement for Human Rights, Lev Ponomaryov.
Nemtsov and Shneider are accused of "intentionally provoking police officers," Moscow Police Department spokesman Viktor Biryukov said, according to Interfax.
Ponomaryov was detained for attempting to organize an unauthorized procession, the Moscow Interior Department told Interfax.
The detentions occurred after the National Flag Day rallies ended in Moscow's Pushkinskaya Square, when some demonstrators continued to march down Novinsky Boulevard to protest plans to cut down part of the city's centuries-old Khimki Forest, Interfax reported.
Ponomaryov told Interfax that he plans to protest his detention.
"I believe it was done on purpose to prevent the action in defense of the Khimki Forest," he said.
Russian authorities say they plan to raze part of the forest to build an $8 billion highway that connects Moscow with St. Petersburg, according to media reports. Protesters say it is possible to construct the road without affecting the forest.
CNN's Maxim Tkachenko contributed to this report.