The head of Wikileaks claims raids on Australian journalists were linked to Julian Assange.

Speaking in London overnight, Wikileaks Editor in Chief Kristinn Hrafnsson said the two cases were connected to US authorities’ attempt to extradited Assange over allegations of soliciting and publishing classified information and of conspiring with former Army private Chelsea Manning to crack a Defence Department computer password, The Australian reports.

Julian Assange is taken to court. (EPA/AAP)

Australian Federal Police (AFP) investigators leave the main entrance to the ABC building located at Ultimo in Sydney, Wednesday, June 5, 2019. Federal police officers have raided ABC's Sydney offices over stories published in 2017 that suggested Australian troops may have committed war crimes. (AAP Image/Bianca De Marchi) NO ARCHIVING (AAP)

“The link is obvious,” Mr Hrafnsson said.

“It is the chilling effect, it is sending a signal, it’s part of the same systemic attack on investigative journalists in reporting on national security issues.”

The raid came off the back of stories published by the ABC in 2017 alleging Australian soldiers may have carried out unlawful killings in Afghanistan, based on leaked Defence papers.

Mr Hrafnsson's allegation come as the US government formally submitted an extradition request to the UK for WikiLeaks founder, according to a US official, for him to face an 18-count indictment.

Julian Assange's exit from Ecuador embassy (AAP)

That indictment, which includes Espionage Act charges, was issued by the Justice Department last month and is pending in federal court in Alexandria, Virginia.

The extradition request had been expected ever since US authorities first announced a criminal case against Assange.

The 47-year-old Assange was evicted on April 11 from the Ecuadorian Embassy in London, where he had been holed up since 2012 after Ecuador granted him political asylum.

He was arrested by British police and is currently serving a 50-week sentence for jumping bail in 2012.

The US government has formally submitted an extradition request to the UK for Julian Assange. (AAP)

Sweden also seeks him for questioning about an alleged rape, which Assange has denied.

Assange was initially charged with a single computer crime violation on allegations that he worked with Manning to crack a government password. Some legal experts have said the additional Espionage Act charges might slow or complicate the extradition process to the extent the UK views them as political offences and therefore exempt from extradition.

The US official spoke on condition of anonymity because the official wasn't authorised to speak publicly.