NSA documents released

The three documents, which US Director of National Intelligence James Clapper said were in "the public interest," explain the bulk collection of phone data, as claimed by NSA whistleblower Edward Snowden.

The documents include reports from 2009 and 2011 on the NSA's "Bulk Collection Program," carried out under the US Patriot Act, the anti-terrorism legislation passed after the September 11 attacks.

The move came as President Barack Obama's national security team testified before Congress on Wednesday, showing how easy it is to use people's phone records to hunt down suspected terrorists.

If the average person intelligence officials are investigating called 40 separate people, the analysis would allow the government to mine the records of 2.5 million Americans when investigating one suspect.

The Obama administration says it is only phone records that are being collected in bulk under the Patriot Act, but it has the option of creating similar databases of people's credit card transactions, hotel records and Internet searches.

Obama has scheduled a meeting with bipartisan lawmakers on Thursday to discuss the NSA's surveillance programs.

New Snowden revelations

Meanwhile, UK daily The Guardian reported that former government systems analyst Edward Snowden had access to a vast online tracking tool that goes far beyond merely accessing telephone data.

The paper, citing documents from Snowden, published National Security Agency training materials for the XKeyscore program, which it describes as the NSA's widest-reaching system that covers "nearly everything a typical user does on the Internet."

According to the report, 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 White House insists that access to such tools is only available to those who are assigned to use them and that multiple "checks and balances" are in place to prevent abuse. "As we've explained and the intelligence community has explained, allegations of widespread, unchecked analyst access to NSA data are false," White House spokesman Jay Carney said.

The NSA also released a statement refuting as false "the implication" that its information collection is "arbitrary and unconstrained."

ng/kms (AP, Reuters, AFP)