MOSCOW (Reuters) - Russian authorities launched criminal proceedings against opposition leader Sergei Udaltsov on Wednesday, accusing him of planning "mass disorder" in protests against President Vladimir Putin's 12-year rule.

Law enforcement officials were conducting a raid at the house of the protest leader, known for his shaven head, leather jacket and hoarse-voiced speeches. Searches were going on at the houses of associates facing the same charges.

Left Front opposition movement leader Sergei Udaltsov (C) arrives at the the Investigative Committee in Moscow October 11, 2012. REUTERS/Maxim Shemetov

The charges, which carry a sentence of up to 10 years in jail, focus on allegations made in a pro-Kremlin documentary that Udaltsov received money and orders from an ally of Georgian President Mikheil Saakashvili to cause mass unrest in Russia.

"The main department of the Investigative Committee opened a criminal case against Sergei Udaltsov ... on the grounds of ... preparing mass disorder," Russia's Investigative Committee said in a statement on its website.

Udaltsov, who has led a series of protests sanctioned by Moscow city authorities, has denied the allegations. Critics say the Kremlin is conducting a politically-motivated crackdown on the leaders of the protests.

The investigative committee, which answers only to the president, also issued a stark warning to protest leaders, who Putin has publicly ridiculed.

"Those who think they can with impunity organise riots, plan and prepare terrorist attacks and other acts that threaten the lives and health of Russians, you underestimate the Russian special services' professionalism," the statement said.

The investigative committee, led by Putin loyalist Alexander Bastrykin, has also pressed charges against opposition leader Alexei Navalny for organising the theft of timber from a state firm. He also faces ten years in prison.

Opposition parliamentarian Dmitry Gudkov, who had led anti-Putin street protests with Udaltsov since late last year, said authorities were seeing how far they could go in cracking down on the protest movement.

"They will be taking the temperature in society. The repressions will continue," Interfax quoted him as saying.

(Reporting by Thomas Grove; editing by Patrick Graham)

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