A judge has ordered that WikiLeaks founder Julian Assange must attend his upcoming court hearing, despite over 200 doctors from 33 countries signing a letter saying his treatment inside Belmarsh Prison has been "psychological torture."

Assange, 48, is currently being held inside south east London's maximum-security prison whilst the court system tries to reschedule an extradition hearing which was postponed due to Covid-19.

But after hearing that Assange was said to be too ill to attend Westminster Magistrates' Court on Monday for the latest administrative hearing in his extradition case, District judge Vanessa Baraitser ruled that he must turn up to the next one unless there is medical evidence to explain why he can not.

The high-profile WikiLeaks founder is wanted in the US to face 17 charges under the Espionage Act and conspiracy to commit computer intrusion after the publication of hundreds of thousands of classified documents in 2010 and 2011.

Last week, the Doctors for Assange group accuse UK and American officials of "intensifying Julian Assange's psychological torture" and call for his immediate release.

The letter, signed by over 200 doctors and printed in The Lancet, says British public officials should be held accountable for their crimes.

Earlier this month, the 48-year-old was said to be too ill to attend the latest court hearing in his extradition case.

At this week's administrative hearing, Assange's barrister Mark Summers QC told the court his client did not appear by video link because he was unwell.

Mr Summers said he was surprised US authorities issued a new and wider indictment last week against Assange, whom they are seeking to extradite from Britain.

He said: "We are to say the least surprised by the timing of this development."

Assange's legal team had heard about the latest indictment through the press and is waiting to be served with it, he said.

The judge told the court that the final hearing is likely to be held at the Old Bailey in September.

She said this has not been confirmed but it "is almost certainly to be held at the Central Criminal Court".

In adjourning the case to July 27 at 10am, the judge said Assange must appear via video link "unless there is medical evidence" to explain his non-attendance.

His full extradition hearing is set to take place on September 7, having originally been scheduled for May 18.