The US Department of Justice (DoJ) has announced 17 new criminal charges against Julian Assange, including Espionage Act charges connected with publishing classified material.

It said the WikiLeaks founder unlawfully published the names of classified sources and conspired and assisted ex-Army intelligence analyst Chelsea Manning in obtaining access to classified information.

Assange, 47, is currently serving a jail sentence in the UK for breaching bail conditions and faces extradition.

He was found guilty last month after his dramatic arrest at the Ecuadorian Embassy in London, where he had sought refuge since 2012 over sexual assault allegations in Sweden. He denies he committed any crimes.

The superseding indictment comes a little more than a month after the Justice Department unsealed a narrower criminal case against Assange.

He was charged with conspiring with Manning to gain access to a government computer as part of a 2010 leak by WikiLeaks of hundreds of thousands of US military reports about the wars in Afghanistan and Iraq.

"The Department takes seriously the role of journalists in our democracy," Assistant Attorney General for National Security John Demers said, adding that the DoJ is not targeting journalists.

He and other officials said they only charged Assange with publishing a narrow subset of material that included the names of sources, including people who risked their lives talking to the US government.

Swedish authorities are separately Assange after they reopened the sexual assault case against him.