Konstantin Dolgov, the ministry's human rights spokesman, said Friday the prison sentence was biased and methods used to bring Bout to the United States questionable, RIA Novosti reported.
A federal judge in New York Thursday sentenced Bout to 25 years in prison for selling weapons he intended to be used to kill Americans. The so-called merchant of death was convicted in November on charges of arms trafficking and terrorism conspiracy.
"We have closely monitored the investigative process and can say for sure that physical and psychological pressure was used against Bout," Dolgov said. Russian officials believe Bout "was actually kidnapped ... and extradited to the United States," he said.
Authorities took Bout into custody in Thailand in March 2008 in a Drug Enforcement Administration sting that used informants posing as representatives of a Colombian terrorist group, the Revolutionary Armed Forces of Colombia.
"In spite of the unreliability of the evidence, the illegal character of his arrest involving the participation of U.S. special service agents in Thailand and the subsequent extradition, American legal officials, having carried out a political order, ignored the arguments of lawyers and numerous appeals from all levels in defense of this Russian citizen," the ministry said.
The ministry will "take whatever action necessary" to repatriate Bout within the bounds of international law, Dolgov said.
Douglas McNabb, an international criminal defense lawyer in Washington, told RIA Novosti Russia may push to have Bout's extradition from Thailand to the United States annulled.
If there is a trial and a court rules the extradition was illegal, McNabb said, "the Thai government will be entitled in accordance with the U.S.-Thai extradition treaty to legitimately demand Bout's return."