The Obama administration has defended its secret collection of millions of telephone records from at least one carrier as part of US counterterrorism efforts.

The admission on Thursday has reignited a debate over privacy as it called the practice critical to protecting Americans from attacks, but White House spokesman Josh Earnest said a court order allowing the government to secretly collect millions of US citizens' telephone records was a critical tool to fight security threats

The admission came after Britain's newspaper The Guardian published on Wednesday a secret court order related to the records of millions of Verizon Communications customers.

The surveillance appears to have involved the phone records of millions of Americans. 

The National Security Agency is collecting the telephone records of millions of US customers of Verizon under a top secret court order, The Guardian said.

The paper said on Wednesday the order was granted by the secret Foreign Intelligence Surveillance Court on April 25 and was good until July 19.

The order requires Verizon, one of the nation's largest telecommunications companies, on an "ongoing, daily basis" to give the NSA information on all telephone calls in its systems, both within the US and between the US and other countries.

The Guardian said the document, a copy of which it had obtained, shows for the first time that under the Obama administration the communication records of millions of US citizens were being collected indiscriminately and in bulk, regardless of whether they were suspected of any wrongdoing.

The Associated Press could not authenticate the order because documents from the court are classified.

Ed McFadden, a spokesman for Verizon, said on Wednesday the company had no comment.

The White House declined comment and referred questions to the NSA. The NSA had no immediate comment.

But Al Jazeera's Patty Culhane said she had confirmed the NSA allegations with a senior administration official.

Under the terms of the order, the phone numbers of both parties on a call are handed over, as is location data, call duration, unique identifiers, and the time and duration of all calls.

The contents of the conversation itself are not covered, The Guardian said.

The broad, unlimited nature of the records being handed over to the NSA is unusual. FISA court orders typically direct the production of records pertaining to a specific named target suspected of being an agent of a terrorist group or foreign state, or a finite set of individually named targets. NSA warrantless wiretapping during the George W Bush administration after the 9/11 attacks was very controversial.

The FISA court order, signed by Judge Roger Vinson, compelled Verizon to produce to the NSA electronic copies of "all call detail records or telephony metadata created by Verizon for communications between the United States and abroad" or "wholly within the United States, including local telephone calls", The Guardian said.

The law on which the order explicitly relies is the "business records" provision of the USA Patriot Act.

Source: Agencies