London, UK - The US government has won the latest round in its High Court bid to appeal against the decision not to extradite Julian Assange on espionage charges.

WikiLeaks founder Assange (50) is wanted in the United States on allegations of conspiracy to obtain and disclose national defense information, following WikiLeaks' publication of hundreds of thousands of leaked documents relating to the Afghanistan and Iraq wars.

After a multi-week hearing, District Judge Vanessa Baraitser ruled in January that Assange should not be sent to the US while also denying him bail, citing his real risk of suicide.

The US government was previously allowed to appeal against her decision on three grounds, including that it was wrong in law.

On Wednesday, the US made a bid at the High Court in London to expand the basis that can be used for its main appeal against the district judge's decision.

The US authorities said they should be allowed to argue two further points - that the district judge was wrong in how she assessed evidence about Assange's risk of suicide, and also appeal against the use of evidence from a psychiatrist who they said "misled" the court.

Lord Justice Holroyde ruled in favor of the US authorities after he found the two points were "at least arguable" at the upcoming main appeal, which will take place over two days in October.

The WikiLeaks founder appeared at the hearing by video-link from Belmarsh Prison, wearing a dark face covering and a white shirt, with what appeared to be an untied burgundy tie draped around his neck.

Dozens of Assange's supporters, including his partner Stella Moris, gathered outside the Royal Courts of Justice on Wednesday morning, chanting and waving signs.

Clair Dobbin, council for the US, had told the court there is a "need for anxious scrutiny" of Assange's reported mental health.

She said part of the US government's appeal will focus on the requirement in law that an individual must be "so ill" that they are unable to resist suicide for a decision to be taken not to prosecute – or in Assange's case, extradite – them.

"It really requires a mental illness of a type that the ability to resist suicide has been lost," she said. "Part of the appeal will be that Mr Assange did not have a mental illness that came close to being of that nature and degree."

Both sides will now prepare for the full appeal, which will be heard in person on October 27 and 28.

If Assange is extradited, the US has said it would consent to him being transferred to Australia to serve any prison sentence he may be given.