Julian Assange allegedly “put lives at risk” with the release of unredacted classified documents, the High Court has been told by lawyers for the United States.

The WikiLeaks founder faces prosecution in the US over an alleged conspiracy to obtain and disclose national defence information following the publication of hundreds of thousands of leaked documents relating to the Afghanistan and Iraq wars.

In a January 2021 ruling, then-district judge Vanessa Baraitser said that Assange should not be sent to the US, citing a real and “oppressive” risk of suicide, while ruling against him on all other issues.

But later that year, US authorities won their High Court bid to overturn this block, paving the way towards Assange’s extradition.

Lawyers for the 52-year-old are now asking for the go-ahead to challenge the original judge’s dismissal of other parts of his case to prevent his extradition.

However, US authorities are opposing Assange’s bid for an appeal, telling the court his case is “unarguable” and should not be allowed to proceed to a full hearing.

At the start of the arguments on behalf of the US on Wednesday, Clair Dobbin KC said the plans to extradite and prosecute Assange are based on his alleged actions, not his political opinions.

She told the High Court in London that Assange faces allegations he encouraged and assisted Chelsea Manning in obtaining classified documents, including around 400,000 Iraq war-related activity reports and 250,000 US State Department cables, before publishing many of them through WikiLeaks.

Ms Dobbin said there were “profound consequences”, with some of the named sources in the documents, who had provided information to the US, facing arrest, the loss of assets, threats and harassment.

“This wasn’t a slip, or an error, this was the publication of a vast amount of material unredacted,” she said.

In written submissions, Ms Dobbin and James Lewis KC described the leak as “one of the largest compromises of classified information in the history of the United States”.

They continued: “It is specifically alleged against the appellant that by publishing this information on the WikiLeaks website, he created a grave and imminent risk that the human sources named therein would suffer serious physical harm.”

The US authorities have denied that the decision to extradite or prosecute Assange is due to his political opinions.

Ms Dobbin said: “The administration in the US of course changed during these proceedings… but nonetheless the prosecution of the appellant remains in foot.

“Because it is based on law and evidence, not political inspiration.”

The barrister later said that the original judge “rejected outright” that Assange should be treated like a journalist “or what he did could fall under the ambit of responsible journalism”.

During the first day of the hearing on Tuesday, Mark Summers KC argued the US prosecution of Assange would be retribution for his political opinions, meaning it would be unlawful to extradite him under UK law.

He said: “This is a paradigm example of state retaliation for the expression of political opinion.

“The district judge did not address it – had she done so, it would have been fatal to her decision.”

Mr Summers later told the court that the US authorities had allegedly developed a “breathtaking” plan to either kill or kidnap Assange while he was in the Ecuadorian embassy, where he remained for around seven years.

The barrister later said the plan “only fell apart when the UK authorities weren’t very keen on the thought of rendition, or a shootout, in the streets of London”.

Edward Fitzgerald KC, also for Assange, later said he is being prosecuted for an “ordinary journalistic practice”.

The hearing before Dame Victoria Sharp and Mr Justice Johnson is due to conclude on Wednesday with their decision on whether Assange can bring the appeal expected at a later date.