The US director of national intelligence has released three declassified documents that authorised the bulk collection of telephone data, one of the surveillance programmes revealed by former spy agency worker Edward Snowden.
The Office of the Director of National Intelligence said in a statement the declassification was made in the "interest of increased transparency".
The documents that were declassified on Wednesday include the 2009 and 2011 reports on the National Security Agency's "Bulk Collection Program" under the USA PATRIOT Act.
In addition it released an April, 2013 order from the Foreign Intelligence Surveillance Court which described how the data should be stored and accessed.
Meanwhile, the deputy director of the NSA said on Wednesday that no one had been fired and no one had offered to resign over Snowden's ability to take large amounts of classified data from agency computers.
"No one has offered to resign. Everyone is working hard to understand what happened," John Inglis said at a Senate Judiciary Committee hearing.
Democratic Senator Patrick Leahy, chairman of the committee, questioned Inglis sharply about how Snowden had managed to take the data.
"I realise you have to have a considerable amount of trust. But don't you have people double-checking what somebody's doing?" he asked.
Inglis said the NSA did not yet know how its safeguards had failed and expected to discover that "over weeks and months".
Snowden's father speaks
Leahy and the Obama administration also clashed over how many terrorist plots might have been thwarted through the secret collection of Americans' phone records since 2006.
Leahy said a list of the relevant plots provided to Congress does not reflect dozens or, as he said, "let alone 54 as some have suggested".
Inglis said the phone surveillance contributed to disrupting or discovering attacks 12 times. Inglis said the 54 involved both the phone records programme and a separate initiative gathering Internet data.
Al Jazeera's Rosiland Jordan reporting from Washington said that both Republicans and Democrats are questioning the legality and appropriateness of this operation and whether such search programs are really necessary.
The developments came as Snowden's father told a Russian television channel that he was willing to agree to a request by the FBI to fly to Moscow to see his son.
Speaking to the state-owned Rossiya 24 channel in footage broadcast on Wednesday, Lonnie Snowden of Allentown, Pennsylvania, thanked Russian President Vladimir Putin and his government for the "courage" they have shown in keeping his son safe.
Addressing his son, Lon Snowden said that "your family is well and we love you".
He added: "I hope to see you soon, but most of all I want you to be safe."
Source: Al Jazeera and agencies