Updated

Russian investigators say a prominent opposition activist has been charged with fraud and money laundering amid growing pressure on President Vladimir Putin's opponents.

Alexei Navalny, who made his name exposing rampant corruption in state-controlled companies, spearheaded a series of street rallies in Moscow that drew up to 100,000 people and followed last December's fraud-tainted parliamentary vote.

Russia's top investigation agency said Thursday that Navalny and his brother Oleg were charged with allegedly defrauding a transportation company of $1.8 million by overcharging it for postal services.

Alexei Navalny, a 36-year-old lawyer, said in an ironic tweet that the charges are "the end of me." He said earlier that the charges are a reprisal for his efforts to mobilize opposition to Putin.