Russian opposition leaders urged President Vladimir Putin on Wednesday to stop clamping down on dissent and warned they would ask Western governments to freeze assets of Russian officials involved in a spiraling crackdown on the opposition.

Alexei Navalny and other opposition activists who were elected to the opposition's Coordinating Council in a weekend online ballot accused the Kremlin of unleashing a campaign of "direct and forceful pressure against its opponents in rude violation of Russian and international law."

They pointed at what they said was the abduction of opposition activist Leonid Razvozzhayev from neighboring Ukraine as an example of the repression of dissenters. The opposition leaders warned that government officials and law-enforcement officers will face "imminent punishment for their crimes against Russian citizens."

They said the opposition will hold a rally in Moscow in support of Razvozzhayev and other jailed opposition members this weekend.

"The Coordinating Council will demand the arrest of all foreign assets of the masterminds and perpetrators of the abduction, torture and illegal criminal repression against the opposition," the opposition leaders said in a statement.

Russia's top investigative agency formally charged Razvozzhayev on Tuesday with orchestrating riots. The agency said he had turned himself in, but Razvozzhayev and his supporters said he was kidnapped from Ukraine where he was seeking asylum, smuggled back into Russia and tortured into confessing that he organized riots.

Members of a Russian prisoners' rights watchdog, who spoke Wednesday after meeting with Razvozzhayev in jail, said unidentified abductors forced him to make "confessions" by threatening to kill him and his family.

Valery Borshchev and other members of the Public Observation Commission said the masked men who abducted Razvozzhayev kept him in handcuffs and leg chains in a basement for three days, denying him food, water, sleep and a toilet until he signed the confessions.

"They accompanied it all with threats, telling him that they know everything about his children and that his children and his wife will be dead," Borshchev said.

Borshchev's colleague, Lidiya Dubikova, said Razvozzhayev looked anemic and his speech was slow, as if he had been drugged. Razvozzhayev told rights defenders that he feared the men who forced him to make confessions would return.

Amnesty International said Wednesday that the claims about Razvozzhayev's abduction and torture "are extremely disturbing" and urged Russia to "ensure such allegations are promptly, effectively and independently investigated."

Charges against Razvozzhayev stemmed from hidden camera footage aired earlier this month by a Kremlin-friendly TV channel. The documentary claimed that leftist leader Sergei Udaltsov met with a Georgian lawmaker to raise money for organizing riots in Moscow and several other Russian cities. Udaltsov rejected the charges and said the footage was a sham.

Udaltsov already was questioned last week and he fears arrest. One of his aides was arrested last week.

Opposition and rights activists denounced the case against Udaltsov and other activists as a throwback to the times of Soviet-era repression. "The evidence of abduction and torture of Razvozzhayev is like a message from hell," gallery owner Marat Gelman wrote in his blog.

Putin has methodically raised the pressure on the opposition since he was sworn in for a third term in May. Protest leaders have faced interrogations, searches and criminal charges, and the Kremlin-controlled parliament churned out a series of repressive bills to discourage people from joining protests and to introduce new tough restrictions on non-government organizations.

On Tuesday, Russian lawmakers passed a new bill offering a new broad definition of treason, which rights activists say is so loose that it could allow officials to brand any dissenter a traitor. Earlier this month, Moscow declared an end to the U.S. Agency for International Development's two decades of work in Russia, saying the agency was using its money to influence elections — a claim the U.S. denied.

And despite an international outrage against the two-year prison sentence given to members of the Pussy Riot punk band for an irreverent anti-Putin protest at Moscow's main cathedral, two of them were sent to remote prison colonies this week. The third one was released after a court suspended her sentence.