The father of Wikileaks founder Julian Assange has said his son’s extradition to the United States to face a slew of espionage charges would be “a death sentence,” while the built-up anxiety from the nearly decade-long saga continues to take a toll on his health.

Assange, 48, is being held in London’s Belmarsh Prison as he fights an extradition request from the U.S., where he faces 18 counts for his alleged role in scheming to hack a government computer and releasing thousands of classified documents.

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“The ceaseless anxiety that Julian’s been under for now 10 years has had a profoundly deleterious effect,” Assange’s father, John Shipton, told BBC television on Tuesday.

“I imagine that he will be really worried because being sent to the United States is a death sentence.”

Last October, concerns grew over Assange’s health during his failed bid to delay the extradition at a hearing where he appeared to struggle to recall his age and name. A month earlier, 60 doctors wrote to the British government expressing concerns about Assange’s health and his fitness to stand trial.

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On Tuesday, Assange’s spokesman Kristinn Hrafnsson told reporters that Assange’s health is improving and he is no longer being held in solitary confinement, Reuters reported.

“I saw him about 10 days ago,” Hrafnsson said at a news conference. “He has improved thanks to the pressure from his legal team, the general public, and amazingly, actually from other inmates in Belmarsh Prison to get him out of isolation.”

Assange spent almost seven years holed up in the Ecuadorian Embassy in London, where he sought shelter in 2012 to avoid extradition to Sweden over a rape investigation which has since been dropped.

Last April, Ecuador withdrew his asylum status, allowing British police to arrest and drag him out of the embassy.

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The extradition hearing is set to begin next week.

The Associated Press contributed to this report.