The US National Security Agency (NSA) is collecting the telephone records of tens of millions of Americans, according to the Guardian newspaper.

The newspaper published what it said was a secret court order directing the Verizon company to hand over data on its customers on an “ongoing” basis.

Civil liberties groups said the details of the report were “stunning”.

The White House broadly defended the practice as a “critical” security tool but did not confirm the report.

US authorities need the information to protect the nation from terrorist threats, a senior Obama administration official told the BBC.

The official said such records allowed counterterrorism officials “to discover whether known or suspected terrorists have been in contact with other persons who may be engaged in terrorist activities, particularly people located inside the US”.

The security agencies and Verizon have not commented.

The US Center for Constitutional Rights said it appeared to be “the broadest surveillance order to ever have been issued”.

The document published by the Guardian was signed by Judge Roger Vinson of the secret Foreign Intelligence Surveillance Court on 25 April and lasts until 19 July.

It falls under a section of the Bush-era Patriot Act which allows access to business records for “foreign intelligence and international terrorism investigations” – it was unclear whether it was a one-off order or a renewal of an existing request.

The order requires Verizon – one of the largest phone companies in the US – to disclose to the NSA the metadata of all calls it processes, both domestic and international.

Such metadata includes telephone numbers, calling card numbers, the serial numbers of phones used and the time and duration of calls. It does not include the content of a call or the callers’ addresses or financial information.

The senior Obama administration official emphasised to the BBC that “on its face” the court order printed by the Guardian did not authorise US government agents to listen in on Americans’ telephone conversations.

The order also contains a gagging order, requiring that “no person shall disclose to any other person that the FBI or NSA has sought or obtained tangible things under this Order”.