Julian Assange was spied on by the US intelligence service during his time in London.
A Spanish private security company hired to protect the Ecuadorian embassy fed information back to the US government when the WikiLeaks founder was a resident there.
A report in Spanish newspaper El Pais said the company, UC Global SL, allegedly handed over audio and video to the CIA of meetings Assange held with his lawyers.
The company is being investigated over the claims by Spain’s High Court, the Audiencia Nacional, said the report.
Assange filed a criminal complaint himself, in which he accused the company of violating his privacy and the secrecy of his client-attorney privileges.
El Pais said UC Global SL had failed to respond to requests for comment on the claims.
In April, Assange was dragged out of the embassy after being handed over to the British authorities by Ecuador.
He took refuge there in 2012 while on bail and facing extradition to Sweden on sex charges, saying he feared extradition to the US if he left over the activities of WikiLeaks.
The US formally requested his extradition in June on 18 charges, including computer misuse and the unauthorised disclosure of national defence information.
He is accused of working with former US army intelligence analyst Chelsea Manning.
He is now in Belmarsh prison in London after being jailed for violating bail conditions imposed over the Swedish extradition request and was due to be released last week, but was remanded in custody pending a hearing of the US extradition case in London in February 2020.
In May, Swedish prosecutors reopened their investigation into an allegation of rape against Assange – an allegation he has always denied.
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