The UK's intelligence-gathering agency "spied" on people who contacted WikiLeaks, the whistleblowing website's founder claims.
Julian Assange says new documents reveal the Cheltenham-based listening post was engaged in "hostile monitoring" of the publisher's website.
Information from national security whistleblower Edward Snowden detailed the spying efforts against WikiLeaks undertaken by GCHQ and the US National Security Agency, he said on Tuesday.
A document dated 2012 revealed that GCHQ spied on WikiLeaks and its readers, said Assange, who has been living at the Ecuadorean Embassy in London since the summer of 2012 for fear of being extradited to the US.
He said: "WikiLeaks strongly condemns the reckless and unlawful behaviour of the National Security Agency. We call on the Obama administration to appoint a Special Prosecutor to investigate the extent of the NSA's criminal activity against the media including WikiLeaks and its extended network.
"News that the NSA planned these operations at the level of its Office of the General Counsel is especially troubling. No less concerning are revelations that the US government deployed 'elements of state power' to pressure European nations into abusing their own legal systems, and that the British spy agency GCHQ is engaged in extensive hostile monitoring of a popular publisher's website and its readers.
"The NSA and its UK accomplices show no respect for the rule of law."
WikiLeaks said it was surprised at the "sweeping" scale of the monitoring as well as the "blatant" way information was gathered.
The organisation said there should be an investigation into the activities of GCHQ.
"There seems to be a lack of interest in the UK to scrutinise the activities of GCHQ," said a spokesman.
WikiLeaks said one of the new documents showed that GCHQ used its surveillance system to secretly monitor visitors to its site.