Julian Assange remains in Ecuador's embassy in London while the Ecuadorian government assesses his application for political asylum.

Julian Assange remains in Ecuador's embassy in London while the Ecuadorian government assesses his application for political asylum. Photo: Reuters

THE head of the United States Senate's powerful intelligence oversight committee has renewed calls for Julian Assange to be prosecuted for espionage.

The US Justice Department has also confirmed WikiLeaks remains the target of a criminal investigation, calling into question Australian government claims the US has no interest in extraditing Mr Assange.

"Mr Assange should be prosecuted under the Espionage Act [of 1917]," the chairman of the Senate Select Committee on Intelligence, Californian Democrat Senator Dianne Feinstein, said in a written statement provided to The Age.

"I believe Mr Assange has knowingly obtained and disseminated classified information which could cause injury to the United States. He has caused serious harm to US national security, and he should be prosecuted accordingly."

Senator Feinstein's call for the Obama administration to move ahead with plans to prosecute Mr Assange came as US Justice Department spokesperson Dean Boyd publicly confirmed that "there continues to be an investigation into the WikiLeaks matter''.

Mr Assange remains in Ecuador's embassy in London while the Ecuadorian government assesses his application for political asylum.

President Rafael Correa said on Saturday that his government had no deadline for a decision.

''That decision will be absolutely sovereign and … [show] respect for human rights," President Correa said.

Mr Assange presented himself at the Ecuadorian embassy on June 19 and has defied a British police order to turn himself in for extradition to Sweden, where he is sought for questioning in relation to sexual assault allegations.

He fears a hostile political climate in Sweden will lead to his ultimate extradition to the US.

In a statement last Friday, one of Mr Assange's lawyers, Susan Benn, highlighted evidence of the existence of a secret US grand jury investigation targeting Mr Assange and other "founders or managers" of WikiLeaks.

Senator Feinstein, who enjoys access to the most secret US intelligence briefings, has argued that Mr Assange should not be protected by the First Amendment free speech provisions of the US constitution.

"Mr Assange claims to be a journalist and would no doubt rely on the First Amendment to defend his actions. But he is no journalist. He is an agitator intent on damaging our government," Senator Feinstein wrote in the Wall Street Journal in 2010.

Foreign Minister Bob Carr, who has declined to describe Mr Assange as a journalist, claimed last week that there was "not the remotest evidence" of any US government desire to prosecute the WikiLeaks founder.

About 200 Assange supporters braved Melbourne's rain yesterday in a rally supporting his appeal to Ecuador for asylum.

The supporters marched from the State Library to City Square just after noon and heard speeches from WikiLeaks founding member Daniel Matthews, human rights lawyer Lizzie O'Shea and Greens MP Adam Bandt.

With BENJAMIN MILLER, AFP

twitter Follow the National Times on Twitter: @NationalTimesAU