More than 60 doctors have signed an open letter expressing “serious concerns about the physical and mental health of Julian Assange,” who is being held at a high-security British prison.

The founder of WikiLeaks was evicted from the Ecuadoran Embassy in London earlier this year and faces possible extradition to the United States on hacking charges.

The doctors, who hail from the United States, Britain, Italy, Germany, Sweden, Sri Lanka and Australia, demanded Assange be taken to a university teaching hospital for assessment and care and argued he was not fit to stand trial next year. They said years of medical assessments and reports on Assange’s health informed their complaint.

“We wish to put on record, as medical doctors, our collective serious concerns and to draw the attention of the public and the world to this grave situation,” the letter states.

“Were such urgent assessment and treatment not to take place, we have real concerns, on the evidence currently available, that Mr. Assange could die in prison,” the letter continued. “The medical situation is thereby urgent. There is no time to lose.”

The letter was circulated by WikiLeaks, the organization Assange founded, CBS News reported. It was addressed to British Home Secretary Priti Patel and Diane Abbott, the opposition’s shadow home secretary.

Assange lived under asylum at the Ecuadoran Embassy for nearly seven years until April, when Ecuador revoked his asylum on allegations he had used the diplomatic compound as a “center for spying.” He is being held at Belmarsh Prison in London, where he awaits a February trial.

The letter cites multiple reports on Assange’s health over the years, including assessments by Nils Melzer, the United Nations special rapporteur on torture and other cruel, inhuman or degrading treatment or punishment. In May, Melzer and a team of medical experts examined Assange and concluded he exhibited “all the symptoms typical for prolonged exposure to psychological torture,” according to a November report.

The British government pushed back against the claims on Monday. “The allegations Mr. Assange was subjected to torture are unfounded and wholly false,” a government spokesperson said in a statement to The Washington Post. “The UK is committed to upholding the rule of law, and ensuring that no one is ever above it.”

Assange, an Australian citizen, is serving a 50-week prison term for jumping bail in 2012 and fleeing to Ecuador’s embassy after Sweden sought to extradite him as part of a rape investigation. Assange has denied those allegations. Last week, Sweden announced it would drop the rape investigation into Assange after authorities concluded they did not have strong enough evidence to proceed.

But Assange has also been indicted on a U.S. hacking charge, over which he faces potential extradition. Assange is accused of attempting to help former Army intelligence analyst Chelsea Manning obtain a password to unlawfully access classified government information.

After his April arrest, Assange attorney Jennifer Robinson called the charges “a dangerous precedent for all news media."

Read more: