Further details on the scope of secret surveillance conducted by the US National Security Agency were released as a fresh leak of material showed how the agency spies on web browsing by people overseas.
The Obama administration released previously-classified documents showing how the NSA directed the US telecoms company Verizon to hand over customer phone records for a three-month period.
The documents were released by the Office of the Director of National Intelligence at the start of a hearing by the Senate judiciary committee into the controversial surveillance programmes exposed by leaks from US whistleblower Edward Snowden to the media.
As the Senate hearing began, the Guardian newspaper, which first revealed the NSA spying based on Mr Snowden's leaks, published a secret 32-page presentation obtained from the former US intelligence contractor showing how the NSA trawls emails, online chats and internet browsing histories of millions of people.
The programme, known as XKeyScore, allows analysts to mine the content of emails, details on websites visited and any internet searches carried out by users without advance approval of a court.
One presentation published by the Guardian says that the programme covers "nearly everything a typical user does on the internet."
Mr Snowden told the paper in an interview in June that he could from his desk "wiretap anyone, from you or your account, to a federal judge or even the president if I had a personal email."
Government officials released the Verizon order, by the Foreign Intelligence Surveillance Court, to illustrate the legal approval sought by the NSA and the restrictions imposed on the spying.
The wide-ranging order on the phone data shows that the spying agency can review information where there is no connection to foreign terrorism and to make that data accessible for intelligence analysis.
The release of the new documents increased the public and congressional scrutiny on the Obama administration’s spying programmes.
Senators at the committee hearing criticised the decision to release the court order and other once-secret documents should so soon before the committee hearing.