The White House declined to say on Wednesday whether the administration ever briefed the US Congress about a top-secret NSA spy program that, according to documents, allows analysts to to search through huge databases of emails, online chats and the browsing histories without prior authorisation.

The Guardian revealed on Wednesday how the NSA describes in training materials that the program, called XKeyscore, is its "widest-reaching" system for developing intelligence from the internet.

The disclosure, which came from documents provided by whistleblower Edward Snowden, comes as the fallout over US surveillance tactics threatens a deepening problem for the White House.

White House press spokesman Jay Carney said he could not give an assurance that Congress had been informed about the surveillance capability. "I am saying I don't know the answer to that," he said, referring questions to the office of the director of national intelligence.

When pressed, he claimed the Guardian's article contained inaccuracies, adding that "informing people about false claims isn't necessarily what we do". He did not specify which part of the report the White House believes to be inaccurate.

The two senior members of the House intelligence committee also rowed in behind Carney. Mike Rogers, the Republican chairman, and the ranking Democrat Dutch Ruppersberger, condemned the Guardian's disclosures.

"The latest in the parade of classified leaks published today is without context and provides a completely inaccurate picture of the program," they said in a joint statement.

They said XKeyscore was "simply a tool used by our intelligence analysts to better understand foreign intelligence".

At a heated Senate judiciary committee hearing on Wednesday, members the questioned the truthfulness of the US intelligence community,

Patrick Leahy, a Vermont Democrat and chairman of the Senate judiciary committee, said: "We need straightforward answers, and I'm concerned we're not getting them."

Leahy, joined by ranking Republican Chuck Grassley of Iowa, criticised director of national intelligence James Clapper for making untruthful statements to Congress in March about the bulk phone records collection on Americans, and NSA director Keith Alexander for overstating the usefulness of that collection for stopping terrorist attacks.

Grassley called a recent apology to senator Ron Wyden and the intelligence community "especially disturbing".

"Nothing can excuse this kind of behavior from a senior administration official," Grassley said. "Especially on a matter of such importance."

Earlier in the day, under growing pressure to be more open about its surveillance techniques, the US administration voluntarily declassified a number of previously classified documents about the bulk collection of phone records.

They may not be the last classified documents to be released to the public. Carney said Barack Obama had encouraged senior national security officials to "look at programs and see where we can be as transparent as possible".

However, in a testy exchange, he was unable to say whether any members of Congress had been informed about XKeyscore or its capabilities.

According to training materials, XKeyscore allows NSA analysts to mine agency databases by filling in a simple on-screen form giving only a broad justification for the search. The request is not reviewed by a court or any NSA personnel before it is processed.

Asked about whether Congress had been briefed about the program, Carney did not answer, instead repeating the NSA's formal response. "As we've explained, and the intelligence community has explained, allegations of widespread, unchecked analyst access to NSA collection data are false," he said.

"Access to all of NSA's analytic tools is limited to only those personnel who require access for their assigned tasks. There are multiple technical, manual and supervisory checks and balances within the system to prevent those who don't have access from achieving that access."

Pressed on whether lawmakers had been informed about XKeyscore, Carney replied: "Well the question was front-loaded with assertions that I had an answer to."

Asked again whether Congress had been informed, Carney referred the question to the office of the director of national intelligence. However he eventually conceded that he did not know whether lawmakers were made aware of the program.

Previously, the White House said the fact it briefed some members of Congress on the NSA's surveillance programs, such as its bulk collection of phone data, justified the spy agency's work, because lawmakers knowingly authorised its activities.

Some members of Congress have disputed this assertion, saying they never knew how surveillance legislation was being interpreted.