Lawyers representing jailed Kremlin critic Vladimir Kara-Murza said Wednesday that they did not know the dissident's exact location after twice being denied access to the facility where he was supposed to be held.
Rumours are swirling of an upcoming prisoner swap involving Russia and Western countries as numerous high-profile prisoners, including foreigners, have gone missing from Russian prisons where they are serving long terms, in recent days.
"Today a lawyer for Vladimir Kara-Murza for a second day running was not allowed to visit him in a prison hospital. The exact location of the political prisoner is unknown," his lawyer Vadim Prokhorov wrote on Facebook.
Kara-Murza, a 42-year-old joint Russian and British citizen, is serving a 25-year sentence in Siberia for treason and other charges.
He suffers from a nerve disease and was moved to a prison hospital earlier this month for medical checks.
The dissident is being represented by a local lawyer in the Siberian city of Omsk, where he has been imprisoned.
On Tuesday and Wednesday, the lawyer was told he could not visit his client because he was having a medical examination, Prokhorov said.
Such a refusal of access is a "gross violation", Prokhorov said.
Kara-Murza is due to have a public court hearing Thursday in Omsk over a legal appeal. His defence team are demanding he be allowed to participate via video link.
"Court staff and the administration of the prison hospital have already expressed doubts that tomorrow there will be stable video link with Vladimir Kara-Murza," Prokhorov wrote.
"But at the same time, so far they deny that he has been moved from the hospital," Prokhorov wrote.
AFP contacted the Federal Prison Service, who said they could not provide information on a prisoner without an official request to the penal colony.
At least seven Russian political prisoners have been moved from their penal colonies or jails in recent days, according to lawyers and families.
A lawyer for jailed former US marine Paul Whelan, charged with espionage, was also unsure of his location on Wednesday.
Moscow and Washington have both confirmed there are ongoing negotiations over a swap involving US reporter Evan Gershkovich, sentenced to 16 years for espionage earlier this month in a fast-track trial slammed as a "sham" by the White House.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
Featured Video Of The Day
Israel Says It Killed Top Hezbollah Commander Fuad Shukr In Beirut Strike
Russia Adds Putin Critic Alexei Navalny's Wife To List Of "Terrorists" Canada Sanctions 6 Russians Over Putin Critic Alexei Navalny's Death Alexei Navalny May Have Died Of Single Blow To Chest: Is It Possible? UPSC Cancels Puja Khedkar's IAS Selection, Bans Her From Taking Exam Ever Ransomware Attack On Service Provider Hits 300 Small Banks Across India 10 Flights To Delhi Diverted Amid Heavy Rain, Several Areas Waterlogged Late-Night Traffic Chaos In Delhi Due To Heavy Rain. See Affected Areas "Either You Will Survive Or I Will': Uddhav Thackeray To Devendra Fadnavis Mumbai May Lose Over 10% Land By 2040 Due To Rising Sea Levels: Study Track Latest News Live on NDTV.com and get news updates from India and around the world.