A British newspaper has published information leaked by former security contractor Edward Snowden detailing a secret US surveillance system for gathering online data.
The system known as XKeyscore reportedly enables US intelligence to monitor "nearly everything a typical user does on the internet", the Guardian newspaper said.
The programme includes real-time data and suggests analysts could narrow searches through use of so-called metadata also stored by the National Security Agency (NSA), America's electronic intelligence organisation, the newspaper reported.
Intelligence analysts can conduct surveillance through XKeyscore by filling in an on-screen form giving only a "broad justification" for the search and no review by a court or NSA staff, the paper said. Searches can be made through vast databases containing emails, online chats and the browsing histories of millions of individuals.
Mr Snowden has been charged under the US espionage act and had his passport revoked. He has been stranded at Moscow's international airport since leaving Hong Kong more than a month ago.
US releases phone-snooping order
Also on Wednesday the Obama administration released documents on its phone-snooping, as a Senate panel questions intelligence officials about the programme.
The official US documents include a court order describing how data from the programme would be stored and accessed, the BBC reports.
Two reports to US lawmakers on the telephone and email records were also declassified.
But lines in the files, including details on "selection terms" used to search the massive data stores, were blacked out.
Deputy Attorney General James Cole told a Senate judiciary committee hearing on Wednesday that the court order spells out how the government can use call data obtained from telecom giants such as Verizon.
For the first time, the government acknowledged publicly that by using what it calls "hop analysis" it can scour the phone calls of millions of Americans in the hunt for just one suspect.
NSA analysts could use the records of everyone a suspect calls, as well as everyone who contacts the contacts of contacts of the initial suspect.
If the average person calls 40 unique people, such three-hop analysis could allow the government to mine the records of 2.5 million Americans when investigating one suspected terrorist.
NSA deputy director John Inglistold the congressional hearing the phone surveillance helped disrupt or discover attacks 12 times, and the larger number were foiled thanks to both the phone-records snooping and a second programme collecting global internet users' data.
Wednesday's was the first congressional session on the issue since the House narrowly rejected a proposal effectively to shut down the NSA's secret collection of hundreds of millions of Americans' phone records.