Demonstrators protest outside Westminster Magistrates Court in London on Monday where WikiLeaks founder Julian Assange has been attending a case management hearing as he fights extradition to the US. The 48-year-old Australian has been in custody at the high-security Belmarsh prison in southwest London since being dragged from Ecuador's embassy in April. Photo: AFP

More than 100 doctors on Monday called on Britain to end Julian Assange's "torture" in prison pending his extradition on espionage charges to the United States.

The 48-year-old Australian is facing 18 counts in the United States - 17 of them under the Espionage Act - that could see him jailed for 175 years.

Washington's extradition request will start being heard Monday at Woolwich Crown Court. Assange is being held at the neighboring high-security Belmarsh Prison.

A group of 117 physicians and psychologists from 18 nations wrote in a letter to The Lancet medical journal that Assange was being subjected to "torture" in prison.

"We condemn the torture of Assange. We condemn the denial of his fundamental right to appropriate healthcare," they wrote in the scientific magazine.

UN special rapporteur on torture Nils Melzer has repeatedly warned that Assange has begun to exhibit signs of psychological torture.

Assange was briefly transferred from prison to a medical facility last year because of his frail health.

London's Westminster Magistrates' Court has also been forced to postpone a series of preliminary hearings because of Assange's inability to make an appearance by video link.

"Our appeals are simple: We are calling upon governments to end the torture of Mr Assange and ensure his access to the best available healthcare, before it is too late," the group of doctors said.

Assange's seven-year hideout in Ecuador's London embassy dramatically ended when British police dragged him out and arrested him on a US extradition request last April.

He was initially wanted in Sweden in connection with a rape investigation that has now been formally dropped.

But Assange had long suspected that he would eventually be sought by Washington for his decision to publish a trove of classified Pentagon documents detailing alleged US war crimes in Afghanistan and Iraq.

His supporters view him as a fearless exposer of injustices such as torture and alleged war crimes committed by US forces and then covered up.

AFP