Russian opposition leader Alexei Navalny has been placed under house arrest and forbidden from using the internet or receiving visitors.
The house arrest is for two months, but can be extended.
Investigators accused him of violating the terms of a suspended sentence from an earlier case.
Navalny, a leading opposition figure and anti-corruption campaigner, has dismissed the charges against him as ridiculous and politically motivated.
He was given a five-year suspended sentence for the theft of 16m roubles ($450,000; £270,000) from a timber company in 2009.
Officials said he had repeatedly travelled outside Moscow, in violation of the sentence.
He was also charged with resisting arrest at a rally on Monday evening, at which hundreds of other activists were also picked up by police.
Mr Navalny and his supporters published a damning report in January alleging massive corruption regarding preparations for the Sochi Olympics.
Unsanctioned demonstrations have become rare since the government signed anti-protest legislation in 2012, levying heavy fines and sometimes imposing jail terms on protesters.
Critics of Russia's president accuse him of stepping up pressure on dissent in recent weeks, with an eye on upheaval in neighbouring Ukraine.