The US National Security Agency (NSA) is collecting the telephone records of tens of millions of Americans, US officials have confirmed.

The practice, first reported by the Guardian
newspaper, has been used to stop a
"significant" terrorist attack on the US, a senior
congressman said.
On Wednesday, the newspaper published the
secret order directing the Verizon company to
hand over telephone data.
Civil liberties groups said the details of the
report were "stunning".
Senior US Senator Dianne Feinstein on Thursday
confirmed the secret court order was a three-
month renewal of an ongoing practice.
US House intelligence committee chairman Mike
Rogers told reporters collecting Americans'
phone records was legal, authorised by Congress
and had not been abused by the Obama
administration.
He said it had prevented a "significant" attack
on the US "within the past few years" but
declined to offer more information.
Later, White House spokesman Josh Earnest
described the practice as a "critical tool"
enabling US authorities to monitor suspected
terrorists.