Julian Assange's lawyers have filed a court complaint in Spain against a group of Spaniards they allege extorted the WikiLeaks founder whom they say may have been the victim of “espionage”, a source in his defence team said Saturday.

Assange, who for seven years lived holed up in London's Ecuadoran embassy where he had taken refuge to avoid extradition to Sweden on rape accusations, was arrested on April 11 after Quito terminated his asylum.

The 47-year-old founder of WikiLeaks, which exposed everything from US military secrets to the wealthy's tax evasion, is now awaiting sentencing for breaching his British bail conditions in 2012.

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The source, who wished to remain anonymous, said the complaint was against “a group of Spaniards who allegedly engaged in extortion.” The source told AFP the complaint was also against various employees of the embassy and Ecuador's foreign ministry “who could be responsible,” without detailing how.

The source added a probe was ongoing into the alleged extortion, as well as “espionage” that could have taken place against Assange, without giving further details.

According to online daily eldiario.es, four Spaniards have videos and personal documents of Assange which they somehow obtained via an alleged spying system that included security cameras set up in the embassy in London.

The Spaniards allegedly tried to extort three million euros ($3.3 million) out of WikiLeaks not to publish any of it, the report says.

If confirmed, it is unclear how the Spaniards got access to the alleged spying system and were able to get the information about Assange.

It is also unclear whether his lawyers accuse the embassy and ministry employees targeted in the complaint, reportedly made to Spain's top-level National Court, of being behind the alleged espionage.

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The National Court could not comment when contacted by AFP.

The accusations of espionage contrast with Ecuadoran President Lenin Moreno's version of events.

In an interview with the Guardian newspaper, he alleged Assange had himself tried to set up a “centre for spying” in Ecuador's embassy.

Now in prison in Britain, Assange is also fighting a US extradition warrant relating to the release by WikiLeaks of a huge cache of official documents.