The US Justice Department has filed 17 criminal charges against WikiLeaks founder Julian Assange.

It says the Assange unlawfully published the names of classified sources and conspired and assisted ex-army intelligence analyst Chelsea Manning in obtaining access to classified information.

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

Assange was initially 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.

WikiLeaks describes itself as specialising in the publication of "censored or otherwise restricted official materials involving war, spying and corruption".

Assange is now fighting extradition to the United States, after Ecuador in April revoked his seven-year asylum in the country's London embassy. 

He was arrested that day, 11 April, by British police as he left the embassy.

He is now serving a 50-week sentence in a London jail for skipping bail when he fled to the Ecuadorean embassy in 2012.

The decision to charge Assange with espionage crimes is notable, and unusual. 

Most cases involving the theft of classified information have targeted government employees, like Manning, and not the people who publish the information itself.

The Justice Department's quick turn-around with the filing of a more substantial indictment against Assange is not surprising.

Under extradition rules, the United States had only a 60-day window from the date of Assange's arrest in London to add more charges. 

After that, foreign governments do not generally accept superseding charges.