Sergei Udaltsov, who has been thorn in Vladimir Putin's side and has huge support from leftwingers, arrested in dawn raid

Russian investigators have launched a criminal case against a leading opposition figure, prompting widespread fears that the Kremlin's crackdown on dissent has entered a new phase aimed at the movement's leadership.

Sergei Udaltsov, a 35-year-old radical leftwinger who has helped spearhead the mass protests that have rocked Moscow since late last year, is being investigated for provoking mass unrest around Russia, said Russia's investigative committee, an agency similar to the US Federal Bureau of Investigation.

Udalstov is also being investigated for allegedly organising terrorist attacks, it said.

Police wearing black balaclavas raided Udaltsov's Moscow flat at around dawn, before carting the thin shaven-headed activist away for questioning at the investigative committee's headquarters.

"This is tyranny and repression," Udaltsov reportedly told a group of supporters and journalists gathered outside his home before entering a waiting car. "The most important thing, friends, is not to be quiet. Don't remain quiet." Udaltsov could face up to 10 years in prison if charged and found guilty of "organising mass unrest".

The head of a group called the Left Front, Udaltsov has served several short stints in jail over the last two years after convictions for offences ranging from staging illegal protests to administrative violations such as jaywalking, which his supporters say are a way to silence the charismatic leader.

Udaltsov, who has forged ties with the popular Communist party, has toured Russia's distant regions aiming to drum up support for the growing opposition to Vladimir Putin. The authorities are said to fear his links with the country's emasculated trade unions, a potentially large pool of support.

"There is one goal here – to stifle any protest to the maximum," Gennady Zyuganov, leader of the Communist party, told journalists. "There is no one left in the Kremlin to say the word 'no'."

The investigative committee said the state's case against Udaltsov was opened following a report attacking him on the state-run television channel NTV.

The channel has been at the forefront of a propaganda campaign aimed at discrediting the opposition, namely with two documentary-style reports called Anatomy of a Protest. The first expounded on Putin's claims that the opposition was funded by the US state department. The second aired earlier this month and focused almost exclusively on Udaltsov, claiming he was plotting with an alleged revolutionary from neighbouring Georgia to overthrow the Russian state.

Using grainy footage from a hidden camera, NTV claimed to show Udaltsov and two associates – both of whom were also detained on Wednesday and face similar criminal investigations – meeting Givi Targamadze, former head of the Georgian parliament's defence committee and a close ally of the country's president, Mikheil Saakashvili. The group is seen discussing tactics and financing related to the Russian opposition. Udaltsov has denied the allegations.

Sergei Parkhomenko, a prominent journalist and opposition activist, said the state's use of NTV "creates a new situation and opens a sort of new epoch". "The ruling group has gone over a certain psychological barrier… to the open use of the press it controls as a part of the repressive apparatus, an instrument of direct violence against citizens."

"We can now say that NTV … has become a part of the security structure," he said. One of Putin's first acts as president at the turn of the century was raiding NTV and bringing it under state control.

The investigative committee statement on Udaltsov included a stark warning to the tens of thousands of Russians who have taken to the streets to protest at Putin's continuing rule: "I would like to draw the attention of those who thought that in our country you can organise riots, plan and prepare terrorist attacks and other acts that threaten the lives and health of Russians with total impunity: you underestimate the professionalism of the Russian secret services and are badly informed of Russian law, including a criminal code which allows for lifetime imprisonment in such cases," it said.

The investigative committee has also brought charges against Alexey Navalny, a prominent opposition leader, for alleged economic crimes. He faces up to 10 years in prison.

Opposition activists have called a protest for Saturday in support of Udaltsov.