Navalny, the most prominent domestic critic of President Vladimir Putin, is already serving sentences totalling 11-1/2 years for fraud, contempt of court and parole violations, all of which he rejects as trumped-up charges intended to silence him.
"I am a genius of the underworld," said Navalny, who is able to post on Twitter through his lawyers and allies.
"You all thought I had been isolated in prison for two years, but it turns out I was actively committing crimes. Luckily, the Investigative Committee was vigilant and didn't miss a thing."
There was no immediate official confirmation of the new case.
(Reporting by Reuters; editing by Guy Faulconbridge)
