Russian left-wing leader Sergei Udaltsov has been summoned for "questioning" by the Kremlin's powerful Investigative Committee on Wednesday, after a murky documentary film broadcast Friday on the state-run NTV network accused him of plotting to overthrow President Vladimir Putin using funds provided by a Georgian parliamentarian and anti-Putin business exiles in London.

Mr. Udaltsov predicted on his blog Saturday that the film was part of a Kremlin plan to charge him with treason, based on a new law that's working its way through the Russian State Duma that would redefine treason to include almost any political activist who works with foreigners against Russian national security interests as defined by the authorities.

"The existence of any instances of financing from Western intelligence and... of 'coup attempts' would lead toward the opening of highly publicized criminal cases against me," Udaltsov, a veteran left-wing street protester, wrote.

On Monday, the State Investigative Committee summoned Udaltsov to appear and explain the accusations made in the film, after receiving a letter from the deputy chairman of the Federation Council, Russia's Kremlin-appointed upper house of parliament, requesting it to do so.

The makers of the documentary film, "Anatomy of a Protest 2," are not named in the credits, but most experts say it was almost certainly made using surveillance footage of Udaltsov gathered by the FSB security service.

The grainy and shadowy film shows someone who resembles Givi Targamadze, chairman of Georgia’s parliamentary committee for defense and security and a close ally of Georgian President Mikheil Saakashvili, talking in a smoke-filled room with a usually-obscured profile of someone who looks like Udaltsov. The Mr. Targamadze figure suggests a range of wild schemes, including seizing Russia's Baltic enclave of Kaliningrad, activating Chechen rebels to commit terrorist acts in Moscow, and doing "something" to disrupt Mr. Putin's 60th birthday jubilee (which passed peacefully on Sunday).

More substantially, Targamadze appeared to be offering Udaltsov financing of $50 million for protest activities, which would be contributed by disgraced Russian banker Andrei Borodin and other anti-Putin exiles living in London.

"We don't know, at this point, whether this will lead to criminal charges or not," says Violetta Volkova, Udaltsov's lawyer. "I don't think that based on what they have they can open a case. I think it was completely faked. We are considering launching a lawsuit against NTV."

Russian experts say it could be extremely serious. The mechanism being used here, they say, is probably to launder illegal secret police footage through a television documentary, which can then be accepted as evidence after citizens – in this case a group of parliamentarians – ask police to check its veracity.

"It's an old official practice in Russia to use a publication as a pretext for investigation," says Andrei Soldatov, an expert on Russia's security services and editor of the Agentura.ru online journal that focuses on national security issues.

"It hasn't been used for many years, since its potential for abuse is obvious. In this case, we might be looking at a serious attempt to open a probe into the facts of that documentary, which can then be used to open a criminal case against Udaltsov," he says.

The fact that the probe has been opened by the Kremlin's Investigative Committee, a kind of super-police body directly answerable to the president and headed by Putin protege Alexander Bastrykin, is a bad sign, says Mr. Soldatov.

"When we see this happening at the level of the Investigative Committee, it means it's serious," he says. "Just launching a probe means they can legally bring in the FSB and other services, and institute surveillance. It need never actually lead to a criminal case, they can just blanket Udaltsov legally with surveillance of all kinds."

The apparent campaign against Udaltsov comes amid a wave of recent actions that appear to target Kremlin critics, including the expulsion of a leading Duma deputy who joined the protest movement and criminal charges laid against politically disobedient banker and newspaper tycoon Alexander Lebedev over televised fisticuffs he was involved in over a year ago.

Nikolai Petrov, an expert with the Carnegie Center in Moscow, says there's little doubt the NTV film about Udaltsov was made using FSB surveillance tapes, but they might have been transformed into almost anything through the magic of film-making.

"The main goal here is to discredit Udaltsov, and other protest leaders, even if they lack any hard evidence against him," says Mr. Petrov.

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"It's not the same as having to prove something in a court of law. You can just mix up footage, something genuine with something fake, add dramatic music and an authoritative-sounding narration, and it sounds convincing to most people.... Regardless of the final result, the mere announcement of a probe by the Investigative Committee serves the purpose of making people believe the accusations made in the film are real," he adds.

"Using this method, you send the message that anybody's reputation can be destroyed, and it's all perfectly legal."