A Russian opposition activist has told human rights workers who visited him in prison that he was forced to confess to plotting unrest against President Vladimir Putin.
Leonid Razvozzhayev claims he was tortured after being abducted in Ukraine, where he was seeking asylum.
Russian investigators say Razvozzhayev confessed after giving himself up.
Two members of a government-approved citizens' group that monitors conditions in prisons visited Razvozzhayev on October 23. They say he told them he was bundled into a van by masked men in Kyiv and taken to a basement where he was forced to write a confession.
Valery Borshchyov told Dozhd television that he believes Razvozzhayev's assertions.
"There is no doubt that [Razvozzhayev] was tortured," he said. "It is usually thought that torture has to involve beating, blood, and so on, but it is not true. There are other kinds of torture. He told us how he was kidnapped and put in a van, how [the abductors] tied his feet and hands with tape and put a hat on his face so he couldn't see anything."
On October 24, Vladimir Markin, a spokesman for Russia's Investigative Commission, maintained that Razvozzhayev had not made any complaints of wrongdoing.
Markin said that "No official claims about torture, kidnapping or any other type of unlawful actions have been received by the Investigative Committee of Russia from Leonid Razvozzhayev, either at the time the criminal case was opened or while the charges were being filed."
Razvozzhayev went into hiding last week after he was named as a suspect in a criminal case.
Authorities are investigating allegations that opposition figures were plotting mass unrest during anti-Kremlin demonstrations.
The UN refugee agency has confirmed he approached its offices in Kiyv last week seeking international protection.
The allegations were based on footage aired on a pro-Kremlin TV channel.
It allegedly portrays Razvozzhayev, Left Front leader Sergei Udaltsov, and an Udaltsov aide, Konstantin Lebedev, conspiring to provoke violence in Russia in a plot financed by a Georgian official.
Razvozzhayev and Lebedev have been formally charged while Udaltsov is under travel restrictions.
All three could be sentenced to 10 years in prison if convicted.
On October 24, Udaltsov's lawyer, Violetta Volkova, denied a media report that her client was planning to flee.
"[Sergei Udaltsov] is not planning to leave the country," she said. "In any case, he would not be able to do that physically since first -- he is under a written pledge, and second -- being a suspect in the criminal case, he is under constant surveillance which is clearly visible just like in my case. Thus in this situation, besides having no such intentions [to flee], he cannot do so physically. This fake news spread by the "Komersant" [newspaper] falls on the conscience of the journalist who wrote it."
Markin told reporters that Udaltsov has been asked to come to the committee on October 26 to be formally charged.
With reporting by Reuters, AFP, and Interfax