Sergei Udaltsov, leader of the opposition Left Front movement, told state-run news agency RIA Novosti that he'd been summoned by investigators looking into a low-quality video that allegedly shows him discussing revolutionary ambitions with political leaders from Georgia.
"It's not a criminal case yet. They are carrying out inquires," he said. "But I have nothing to hide."
He added the footage was a forgery, saying it's part of a "wave of repression" launched by the Kremlin.
Arrested on several occasions for his opposition activity, Udaltsov told the Russian bureau of Radio Free Europe/Radio Liberty in September there should be early elections to unseat President Vladimir Putin. State Duma elections in December and presidential elections in March, he said, were illegitimate.
Putin's re-election this spring to a third non-consecutive term sparked widespread unrest in Russia. More than 600 people were arrested after demonstrators clashed with Moscow police during May 6 demonstrations.