London (AFP) - Britain's High Court on Wednesday finished hearing two days of arguments over whether to grant WikiLeaks founder Julian Assange a fresh appeal against his extradition to the United States to face espionage charges.

Two senior judges heard evidence from his lawyers and those representing Washington, and opted against making an immediate decision on what is likely Assange's final UK bid to block extradition.

"We will reserve our decision," judge Victoria Sharp said as the latest legal proceedings in the long-running case concluded. It is unclear when she and judge Jeremy Johnson will issue their ruling.

Washington indicted Assange, the Australian founder of WikiLeaks, multiple times between 2018 and 2020 over its publication of hundreds of thousands of secret military and diplomatic files on the US-led wars in Iraq and Afghanistan.

Assange has since waged a half-decade battle against being sent there, but has lost successive rulings in recent years. If he fails again, he could be extradited within weeks.

Lawyers for the US government urged the court to reject his arguments on various grounds.  

Clair Dobbin said that Assange had "solicited" the secret US files and, in eventually publishing them "indiscriminately" without redactions, that his actions were "unprecedented" and did not constitute journalism. 

"The evidence shows that from the time the appellant started WikiLeaks... he sought to recruit individuals with access to classified information," Dobbin added. "He worked with hackers."

'State-level crimes'

In response, one of Assange's lawyers, Mark Summers, hit out at Dobbin's testimony for failing to address that he was exposing "state-level crimes". 

"We heard no answer at all," he said, adding "that is protected conduct" under UK law. 

Assange was absent from court for the two-day session, and did not follow the proceedings via video due to illness, his lawyer said.

Dozens of his supporters massed outside on both days, demanding that the judges halt his extradition.

His lawyers said Tuesday that the US charges were "political" and that he was being prosecuted "for engaging in ordinary journalistic practice of obtaining and publishing classified information".

Assange's lawyers also argued that the decades-long prison sentence he faces was "disproportionate", accusing Washington of acting in "bad faith" and contravening its extradition treaty with Britain.

US President Joe Biden has faced domestic and international pressure to drop the 18-count indictment against Assange in a Virginia federal court, filed under his predecessor Donald Trump.

Major media organisations, press freedom advocates and the Australian parliament have all denounced the prosecution under the 1917 Espionage Act, which has never been used over the publishing of classified information.

"We call again on the Biden administration to find a political solution to bring this case to a close," Reporters Without Borders said Wednesday, adding that Assange "cannot get a fair trial" in the United States.

'Vast' leak

But in court, Dobbin noted the prosecution had continued under two different presidential administrations because "it is based on law and evidence, not political inspiration".

It had "profound consequences" for both the US and those whose names were disclosed, she added.

If the High Court rules against Assange, he will have exhausted his UK legal options.

His wife Stella Assange has said he would then ask the European Court of Human Rights to temporarily halt the extradition.

This would need to happen within 14 days of losing the appeal bid, his lawyers say.  

The couple, who have two children together, met while Assange was holed up in Ecuador's London embassy for seven years from 2011.

He had fled there to avoid extradition to Sweden, where he faced accusations of sexual assault that were later dropped.

He was arrested by UK police in 2019.

A UK district judge previously blocked his extradition on the grounds he would likely kill himself in US custody. 

But the High Court reversed the decision on appeal in 2021 after Washington vowed not to imprison him in its most extreme prison, "ADX Florence".

It also pledged not to subject him to the harsh regime known as Special Administrative Measures and eventually allow him to be transferred to Australia.

In March 2022, the UK's Supreme Court refused permission to appeal there, arguing that Assange had failed to "raise an arguable point of law".

Months later, the interior minister at the time, Priti Patel, formally signed off on his extradition.