Doctors who examined Julian Assange say his self-imposed exile is having a "dangerous" impact on his health.
Sondra Crosby and Brock Chisholm gave the Wikileaks founder a comprehensive 20-hour medical examination at the Ecuadorian embassy in London in October 2017.
Mr Assange, 46, has lived in the embassy for five-and-a-half years. He sought political asylum in 2012, after an extradition request from Sweden over sexual assault allegations.
Mr Assange maintains that his self-imposed exile within the confines of the embassy is unrelated to the Swedish investigation and that he wants to avoid deportation to the United States, where he could receive the death penalty for leaking classified information through Wikileaks.
In an article published by The Guardian on Wednesday (local time), Dr Crosby and Dr Chisholm claim that, in their professional opinion, Mr Assange's health is threatened by his confinement.
While they were unable to discuss specific results of the evaluation, due to doctor-patient confidentiality, the clinicians revealed that Mr Assange is in "urgent" need of several tests, treatments and procedures, which are not available to him in the embassy, due to size restrictions.
"Our assessment reveals that he has had no access to sunlight, appropriate ventilation or outside space for over five-and-a-half years," they wrote.
"This has taken a considerable physical, as well as psychological toll."
Rumours of Mr Assange's poor health have circulated during his lengthy stay in the embassy. There have been reports that he has both a serious shoulder issue and a lung problem.
Dr Crosby and Dr Chisholm say he is unable to get the medical attention he requires "due to the threat of imminent arrest, should he step outside the embassy, even for a medical emergency".
"It is unconscionable that Mr Assange is in the position of having to decide between avoiding arrest and potentially suffering the health consequences, including death, if a life-threatening crisis, such as a heart attack, were to occur."
They say that the toll Mr Assange's circumstances have taken on his physical and psychological wellbeing is in violation of the United Nations' rules around the treatment of prisoners.
In 2015, Ecuador requested that Mr Assange be allowed safe passage to a London hospital for a medical examination, which the UK government refused.