Lawyers for Julian Assange are taking action aimed at forcing US President Donald Trump's administration to reveal charges "secretly filed" against the WikiLeaks founder.
The lawyers are also pressing Ecuador to protect Assange from being extradited to the US if he leaves its embassy in London, where he has been living for more than six years.
A 1172-page application has been made to the Washington-based Inter-American Commission of Human Rights (IACHR), asking it to make an "urgent intervention" in the case.
Assange was granted political asylum by the Ecuador government and has remained in the embassy since the summer of 2012, believing he will be extradited to the US if he leaves the building.
Restrictions described by WikiLeaks as an "isolation regime" were placed on his communications and visitors last year.
The move by lawyers on Wednesday follows a mistake in a document filed by the US authorities in an unrelated case last year which suggested criminal charges may have been prepared against Assange in secret.
The Trump administration is accused of refusing to reveal details of charges against Assange despite the fact that sources in the Department of Justice have confirmed he has been charged under seal, his lawyers said.
"The revelation that the US has initiated a prosecution against Mr Assange has shocked the international community", the legal submission stated.
The US government is required to "provide information as to the criminal charges that are imputed to Mr Assange in full," it added.
The submission said that for the first time, US federal prosecutors have formally approached people in the US, Germany and Iceland in recent months and pressed them to testify against Assange in return for immunity from prosecution.
Baltasar Garzon, the international co-ordinator of Assange's legal team, said he was asking the IACHR to make an urgent intervention in Assange's favour.
Garzon said he was calling for international solidarity for this case, in which the right to access and impart information freely was in jeopardy.
The application by Assange's lawyers identifies a raft of legal obligations that the US and Ecuador are "flouting" in their treatment of him.
The lawyers claim the Trump administration has been attempting to "pressure" Ecuador to hand over Assange, including "serious overt threats" against Ecuador made by senior US political figures.
"Ecuador is required to end the regime of isolation imposed on Mr Assange, suspending the application of the so-called special protocol and guaranteeing his rights as an asylee will be respected in full," the document filed by his lawyers stated.
