United States politicians have blasted the nation's intelligence agencies for trampling on privacy rights and vowed to impose limits on the government's authority to scoop up Americans' phone records.

At a House Judiciary Committee hearing, members from both parties berated senior officials over the collection of bulk phone data as beyond the limits of the US Constitution as well as legislation adopted by Congress.

"I think that very clearly, this programme has gone off the tracks legally," said Representative Zoe Lofgren of California.

The hearing focused on the government's far-reaching surveillance activities that have come under intense scrutiny after Edward Snowden revealed the National Security Agency (NSA) was collecting phone "meta-data" of conversations between foreign nationals and American citizens through a programme known as "Prism".

"With these programmes and other intelligence activities, we are constantly seeking to achieve the right balance between the protection of national security and the protection of privacy and civil liberties," Deputy Attorney General James Cole told the committee.



'Serious violation' of law

House representatives, however, said Congress had amended the post-9/11 Patriot Act to ensure phone or other business records would only be collected on a narrow basis, when government agencies had a specific suspect or threat in mind.

"We amended the Patriot Act to avoid this very same problem," said John Conyers, the senior-ranking Democrat on the committee, who called the data collection a "serious violation" of the law.



"This is unsustainable, it's outrageous and must be stopped immediately," Conyers said.

Senior justice and intelligence officials insisted the data mining of phone records was reviewed by a secret court, in line with laws adopted by Congress and only conducted to track down al-Qaeda-linked fighters.

"With these programmes and other intelligence activities, we are constantly seeking to achieve the right balance between the protection of national security and the protection of privacy and civil liberties," Deputy Attorney General James Cole told the committee.

Administration officials told the committee that the phone data allowed spy agencies and the FBI to track down an associate of Najibullah Zazi, who admitted to plotting to bomb the New York City subway.

Court ruling

The pressure came a day after a US court ruled the government must release elements of a 2008 court decision justifying Prism.

The ruling could offer a rare glimpse into how the government legally justified such data collection programmes under the Foreign Intelligence Surveillance Act (FISA).

The government is expected to decide by August 26 which parts of the 2008 opinion may be published, according to a separate court filing by the Justice Department.