MOSCOW - A Russian dissident claimed he was kidnapped last week in neighboring Ukraine by Russian special forces, brought back to Moscow, and beaten until he confessed to a conspiracy against the government.

Leonid Razvozzhayev disappeared in Kiev last Friday, where he was discussing the possibility of asylum at an office of the U.N. High Commissioner for Human Rights. Several days later he appeared in a Moscow prison and investigators displayed a signed confession that admits to conspiring to incite "mass unrest," a crime that carries penalties up to 10 years in prison.

If true, his abduction may signal a dark new chapter in what critics say is the Kremlin's effort to silence an opposition that has staged unprecedented protests against the government of President Vladimir Putin over the past year.

Video posted on a Russian tabloid website earlier this week shows Razvozzhayev shouting at a reporter that he had been tortured. He reportedly claims that masked men were waiting for him after he left an office in Kiev and was thrown in a minivan, bound with his head covered, and driven for hours until he was transferred to another vehicle at what he believes was the border with Russia.

There, Razvozzhayev claims he was interrogated for two days.

"For two days they didn't let me go to the toilet. I didn't eat, I didn't drink the whole time," Razvozzhayev reportedly told a group of prison rights activists who visited him, according to the New Times magazine. He says they threatened to harm his family if he did not confess and implicate other activists.

Ukrainian officials have reportedly confirmed that Razvozzhayev was taken by Russian special forces, but said it was part of an appropriate police action. A spokesman for the U.S. Embassy in Moscow told Interfax the United States is "concerned" about the case and called on Russian authorities to investigate Razvozzhayev's treatment. According to RIA Novosti, Putin's spokesman declined to comment, saying, "This is hardly the kind of thing that the Kremlin can and should comment on."

Razvozzhayev, who is also an aide to an opposition member of parliament, says he arrived in Ukraine on Oct. 15, a day before investigators announced an investigation into him and two other activists, accused of plotting mass unrest and terror attacks in Russia. Also accused was leftist opposition leader Sergei Udaltsov, a vocal Kremlin opponent who led many of the past year's protests.

On Oct. 5, NTV, a pro-Kremlin television station, aired its second documentary that purports to show Udaltsov conspiring with politicians from neighboring Georgia, Russia's arch-nemesis, and planning to incite mass unrest. The film showed grainy footage with a voice they claim is Udaltsov's.

Udaltsov dismissed the allegations, but investigators soon detained him for questioning and are expected to formally charge him, citing the NTV documentary as evidence. His family has reportedly fled to Ukraine, but Udaltsov says he has no plans to leave the country.

This latest episode appears to illustrate a change in tactics after Putin appeared to tolerate the protests that sprang up after parliamentary elections last December that were widely seen as fraudulent and continued throughout his campaign for a third term as president. Despite the wave of protests, unprecedented during his dozen years in power as President and then Prime Minister, Putin won the election in March.

After his inauguration in early May, however, the ruling United Russia party introduced a series of new laws that critics say were aimed at stifling dissent and making it harder for the opposition to operate. They include new laws constricting the ability to gather, restrictions on how foreign-funded NGOs can operate, and most recently broadening the definition of treason.

In what was seen as a bellwether of Putin's patience with dissent, a Moscow court sentenced three young punk feminists from the group Pussy Riot to two years in prison for "hooliganism" after they performed an anti-Putin stunt on the altar of Moscow's Christ the Savior Cathedral in February in which they begged for divine intervention to rid Russia of Putin. One woman was released after an appeal earlier this month, but on Monday the two other women were sent to women's penal colonies east of Moscow that their group described as "brutal." One of them is reportedly sharing a cell with a convicted murder accomplice.

Meanwhile, Razvozzhayev remains in a Moscow prison cell and says he fears for his life. His lawyer has filed requests to annul his confession because he claims it was given under duress.

"I'm scared to stay here alone," he reportedly told the prison rights activists who visited him. "I'm afraid those men, the ones who tortured me, will come back."