US National Intelligence Director James Clapper has apologised for his "erroneous" testimony to lawmakers that the National Security Agency does not collect data from Americans' phone records and internet use.
Clapper had been asked by Senator Ron Wyden at a March 12 Senate panel hearing if the NSA had gathered "any type of data at all on millions or hundreds of millions of Americans", and the spy chief replied: "Not wittingly."
Leaks from former NSA contractor Edward Snowden have since exposed a "data-mining" programme that scoops up telephone records and some internet communications of Americans.
The revelations forced the spy chief to correct what he called his "erroneous" testimony before the panel, according to a letter posted online by his office.
In a letter to the chair of the Senate Intelligence Committee, Senator Dianne Feinstein, Clapper said he wanted to "set the record straight" given the "heated controversy" prompted by his remarks.
Clapper wrote that his answer had mistakenly focused on different intelligence-gathering activities that allow for spying on the content of communications only under specific guidelines and a judge's approval. He said "my response was clearly erroneous - for which I apologise".
Clapper's staff immediately acknowledged the error to Senator Wyden's aides after the hearing but did not issue a public apology as the data collection programme had remained classified until recently, according to the spy chief.
"I can now openly correct it because the existence of the metadata collection programme has been declassified," he said in the letter, which was dated June 21.