Vladimir Kara-Murza, a longtime opposition politician and Pulitzer Prize-winning Washington Post Opinions contributor who is serving a 25-year sentence in Russia for treason because he criticized the war in Ukraine, was being moved from the penal colony where he was being held, prison officials said on Wednesday, to an uncertain destination.

Officials from Russia’s penitentiary service told Reuters that Kara-Murza was being transferred from the colony, IK-6 in the Siberian city of Omsk, but would not say to where. Kara-Murza has been in poor health, but his lawyer, Vadim Prokhorov, said that the defense team could not get access to their client at an Omsk hospital for two consecutive days.

Prokhorov’s statement, on Facebook, added to mounting speculation by lawyers, prisoners’ relatives and journalists that the United States, Germany and potentially other countries are preparing for a sweeping prisoner swap with Russia.

Also this week, at least seven other political prisoners in Russia disappeared from the colonies where they were being held, including opposition figures Ilya Yashin, Lilia Chanysheva and Ksenia Fadeeva, as well as activist Oleg Orlov and artist Alexandra Skochilenko, a move that lawyers described as extremely unusual. In addition to Kara-Murza, two other prisoners were reported to have gone missing Wednesday, bringing to 10 the total number suddenly out of communication.

According to Prokhorov, Kara-Murza is due to appear in court on Thursday, but it is not clear whether the hearing will be held. At the same time, he said, hospital administrators would not confirm that Kara-Murza had been moved.

Plane spotters on Wednesday reported that a special government aircraft, part of the flight squadron “Russia,” which is managed by the presidential administration, visited several regions where the missing prisoners were being held before returning to Moscow, prompting speculation that some of them were moved to the capital.

A lawyer for Paul Whelan, an American former Marine who was convicted of spying in 2020 and is serving a 16-year sentence in Russia, said that she is unaware of his whereabouts and cannot contact him.

“There are rumors about a possible exchange,” the lawyer, Olga Karlova, told the Interfax news agency. “I sent a request to the colony administration, but they are not responding.”

Karlova said she requested that the Public Monitoring Commission, a government body overseeing prisoners across Russia, visit Whelan and establish his whereabouts. Eva Merkacheva, a member of the commission, said the group did not have any information about a potential swap but did not rule it out.

“Could this be a group exchange? Anything is possible,” Merkacheva wrote on her Telegram blog. “This has never happened in modern Russian history, but in Soviet history it did. Could this be a pardon? In the case of some, it could have been (as they wrote a petition to the president), but the rest did not do this.”

Maria Ponomarenko, a journalist serving a six-year sentence for spreading “fakes” about the Russian military, was not brought to a scheduled court hearing on Friday, her employer, RusNews, posted on its Telegram channel.

Prisoners’ relatives and friends said they are unaware of the reasons for the transfers.

A lawyer for one prisoner told The Washington Post on Tuesday that the defense team did not get any heads-up about a potential swap, but “everything looks very unusual and extraordinary; something very unusual is going on.”

“I don’t believe in coincidences; it looks like well-coordinated actions,” the lawyer said, speaking on the condition of anonymity because of concern about legal repercussions for communicating with a foreign news organization.

There was no confirmation from American or Russian officials that the prisoner movements were connected to an exchange. However, senior Russian officials, including Foreign Minister Sergei Lavrov, have said that talks are underway for an exchange that would involve the American journalist Evan Gershkovich, a reporter for the Wall Street Journal, convicted in Russia this month of espionage — charges that he, his employers and the U.S. government say are baseless.

Kremlin spokesman Dmitry Peskov on Wednesday declined to comment on the possibility of a prisoner exchange, as he did the day before when also asked about the speculation.

On Tuesday, Rico Krieger, a German citizen who was sentenced to death after being convicted in Belarus of terrorism, was pardoned in a surprise move by the country’s authoritarian leader, Alexander Lukashenko. Some analysts suggested that Krieger could be involved in a swap as Russia is known to be seeking the release of Vadim Krasikov, an assassin serving a life sentence in Germany.

Russia also holds a 19-year-old dual Russian-German citizen, Kevin Lik, who was recently sentenced to four years for treason. On Tuesday, Lik disappeared from a colony in the remote northern Arkhangelsk region.