A US judge has ruled that the mass collection of the US citizens’ telephone records by the National Security Agency (NSA) is likely to be unconstitutional, labelling the technology behind the programme as "almost-Orwellian".

US District Judge Richard Leon labelled the technology behind the programme as "almost-Orwellian" and that the practic was an "arbitrary invasion".

"I cannot imagine a more ‘indiscriminate’ and ‘arbitrary invasion’ than this systematic and high-tech collection and retention of personal data on virtually every single citizen for purposes of querying it and analysing it without judicial approval," Leon said.

"The government does not cite a single case in which analysis of the NSA’s bulk metadata collection actually stopped an imminent terrorist attack.

"Given the limited record before me at this point in the litigation – most notably, the utter lack of evidence that a terrorist attack has ever been prevented because searching the NSA database was faster than other investigative tactics – I have serious doubts about the efficacy of the metadata collection program as a means of conducting time-sensitive investigations in cases involving imminent threats of terrorism."

Leon also questioned the need of the programme, saying that the government could not mention a single case in which the mass data had stopped a forthcoming attack.

"I have serious doubts about the efficacy of the metadata collection program as a means of conducting time-sensitive investigations in cases involving imminent threats of terrorism," Leon added.

The White House turned down the proposal that NSA whistleblower Edward Snowden had been granted amnesty, and reported that the government had been pressing Russia to return him to the US.

White House spokesman Jay Carney said: "There’s been no change in our position."

"He faces felony charges here, he ought to be returned to the United States, again, where he will face full due process and protection under our system of justice, that we hope he will avail himself of," Carney said.