MOSCOW (AFP) ― Russia charged popular protest leader Alexei Navalny with embezzlement on Tuesday, reviving a case that could land one of President Vladimir Putin’s most vocal critics behind bars for 10 years.

The Investigative Committee said Navalny would also be barred from leaving Moscow during the probe into his role as an unofficial advisor in a timber deal struck by regional officials in 2009 that triggered the charges.

The charismatic 36-year-old corporate lawyer, who rose to prominence as an anti-corruption campaigner, looked pale as he emerged from a meeting with investigators where the charges were upgraded to grave economic crimes.

“Something absolutely absurd and very strange has happened because they have completely changed the story behind the charge,” he told reporters. “I cannot imagine how the investigators can prove this. But probably they will”.

On its website, the committee said a charge of “inflicting material harm,” which risked up to five years in jail, had been changed after new “economic studies,” and Navalny is now charged with organising a criminal group that embezzled money.

The new charge carries up to 10 years in prison.

“It all looks as if Navalny is going to get a jail term of seven years or so,” his lawyer Vadim Kobzev told the RAPSI legal news agency.

Putin, who has faced waves of protests over his election to a third term at the Kremlin, insisted Russia does not use its judicial system to incarcerate activists.

“I can say firmly that there is no such tool nor desire in the state’s political arsenal ― to suppress anyone with prison for their human rights activity,” he said at a youth forum, without mentioning Navalny.

Navalny however said in an interview on independent Dozhd television channel that he was sure decisions to make arrests in political cases are “made directly by Putin.”

He also said there was a possibility of him being charged with organising mass riots during a May 6 protest in Moscow that ended in violence and a probe that has seen 14 people arrested.

“It is being stated rather clearly that they (the investigators) want to have a special probe against riot organisers,” he said.

Navalny became a cult figure in Russia’s growing Internet community with his investigations into state corruption, before helping spearhead the wave of protests that rocked the Kremlin last winter.

He has emerged as one of the most prominent leaders of a splintered protest movement that has faced a crackdown from authorities since Putin’s disputed third presidential term began in May.

The charges are likely to unite the opposition around Navalny, liberal opposition politician Boris Nemtsov said.

“After Navalny was handed 100 percent fabricated charges today, the situation became clearer. Alexei has every chance of heading the opposition,” Nemtsov wrote on Facebook.

The charges relate to a case investigators had previously dropped, but the powerful Investigative Committee chief Alexander Bastrykin this month demanded the case be reopened.

Investigators had originally accused Navalny of causing a loss of 1.3 million rubles ($40,000) to the budget of the Kirov region by advising a local state-owned timber firm to sign a deal with a private company in 2009-2010.

The new charges increased the alleged loss to 16 million rubles ($500,000) and accused Navalny of acting in cahoots with the private timber firm.

The case appears to be an attempt to give Navalny a taste of his own medicine, after he exposed dishonesty in state companies and called the ruling party “the party of swindlers and thieves.”

“Navalny, who has for several years been lecturing the country about someone being a swindler and a thief, has himself been caught out in illegal acts,” a senior ruling party official, Andrei Isayev, said on the party website.

Navalny faced a scrum of television cameras with his usual confident demeanour, but seemed shocked by the harsher charges which he called “mega-strange”.

He admitted he could no longer rule out being arrested in the coming days or weeks.

“If it is possible for them to say that I stole those 16 million (rubles), then anything is possible,” he said.

The United States on Tuesday voiced deep concerns about the charges against Navalny and an all-girl punk band detained for performing an anti-Putin song in Russia’s main Orthodox cathedral.

Washington had “serious concerns about politically motivated prosecutions of the Russian opposition,” State Department spokesman Patrick Ventrell told reporters.

Separately Tuesday, Russian police detained dozens of people in Moscow and Saint Petersburg who staged demonstrations to demand the right to assemble, Russian news agencies reported.

About 25 people were detained for attempting to hold an unsanctioned rally on Moscow’s Triumfalnaya square, police said, though the rights monitoring group Ovdinfo put the number arrested at 45.