Concern is mounting over the condition of a former U.S. Marine who has been held in Russian custody for more than three years, with advocates warning he may not survive much longer without intervention.

Robert Gilman is described as being "at the edge of death" after falling into a dissociative stupor more than six weeks ago, according to Eric Lebson, director of strategy at Global Reach, an organization representing his family. One of his attorneys alleges he has been subjected to physical and psychological torture.

Gilman, a 32-year-old former Marine, was forced to take psychiatric drugs and to lie about an alleged beating his family received and about allegedly abandoning the United States, Lebson told CNN. He was transferred from the hospital at his prison — located about six hours from Moscow — to the psychiatric unit of a civilian hospital, according to Lebson. Lebson said they have received information that Gilman is being fed through a tube and handcuffed to his hospital bed, "despite the fact that he is not physically conscious."

Neither Gilman's attorney nor his mother, who traveled to Russia with a Russian court order permitting her to see her son, has been allowed to visit him since his transfer to the civilian hospital. "The fact that his mother traveled all the way there … and was not allowed to see him seriously concerns us, as he could be dead or in a situation similar to that of Otto Warmbier," Lebson said.

"I am more afraid for my brother than I have ever been since this horrible nightmare began. I am worried about never seeing him again if the Russians do not release him. I am worried he could die," said Lexie Hudson, Gilman's sister. Hudson urged the U.S. government to make clear to Russia that Gilman must be released immediately, adding that "any deal necessary to achieve this is better for the United States and Russia than having to deal with my brother's death because neither country acted with the necessary urgency when there was still time."

The U.S. government said it is deeply concerned about Gilman's health and his prolonged detention in Russia, and a State Department spokesperson said the U.S. has repeatedly raised his case with the Russian government and has requested his release on humanitarian grounds. The family said they were informed that Secretary of State Marco Rubio raised Gilman's case with Russian Foreign Minister Sergei Lavrov during a meeting in the Philippines at the end of July.

Gilman was arrested in January 2022. Russian authorities alleged he was drunk and had an altercation with a police officer, a characterization Lebson disputes, saying Gilman was beaten by police, felt ill, and accidentally kicked an officer. He was sentenced to four and a half years in prison.

Fellow former Marines and ex-Russia detainees Trevor Reed and Paul Whelan issued a statement calling on the White House to take immediate action to bring Gilman home, describing him as part of "a small group" of former Marine ex-hostages of the Russian government who also suffered serious medical complications during unjust detention.

Gilman is one of several Americans still detained in Russia, including Andre Khachatoorian, Olga Jezler, Chuck Zimmerman, David Barnes, Aleksander Antonov, and Stephen Hubbard — though only Hubbard has been formally designated as wrongfully detained by the U.S. State Department.

Whether Gilman's mother or legal representatives will be granted access to him, and whether the U.S. government will pursue a formal wrongful-detention designation or a prisoner exchange, remains unresolved.