Russian authorities this week confirmed opposition supporter Leonid Razvozzhayev was in custody. He allegedly confessed to supporting a plot to overthrow the government alongside opposition leader Sergei Udaltsov.
He was quoted by Russia's state-run news agency RIA Novosti as saying while leaving a Moscow courthouse that he was abused by authorities.
"They tortured me for two days, they kidnapped me in Ukraine," he said. Vladimir Markin, a spokesman for a Russian investigative committee, said Razvozzhayev was in his "right mind" when he signed a confession, however.
A spokeswoman for the U.N. High Commissioner for Refugees in Ukraine told the BBC that Razvozzhayev had disappeared from Kiev following a meeting with U.N. officials. Razvozzhayev and Udaltsov were connected to an alleged coup plot alongside a politician in Georgia.
Opposition to Putin has grown since he secured a non-consecutive third-term in office in an early 2012 election viewed by some monitoring groups as fraudulent.