October 29, 2013 - 10:02 AMT
PanARMENIAN.Net - Pressure is growing on the White House to explain U.S. intelligence gathering and why President Barack Obama appeared not to know the extent of operations, according to BBC News.
The intelligence agency head and other officials are to testify before the House of Representatives later.
And the chair of the Senate's intelligence committee called for a "total review" of U.S. spying programmes.
The president has spoken publicly of his intent to probe spying activities amid claims of eavesdropping on allies.
An EU delegate in Washington has described the row over intelligence gathering as "a breakdown of trust".
In a U.S. television interview, President Obama said that national security operations were being reassessed to make sure the National Security Agency's (NSA) growing technical spying capability was kept under control.
"We give them policy direction," he told ABC's Fusion network.
"But what we've seen over the last several years is their capacities continue to develop and expand, and that's why I'm initiating now, a review to make sure that what they're able to do, doesn't necessarily mean what they should be doing."
White House spokesman Jay Carney earlier told reporters that the administration "recognise[s] there needs to be additional constraints on how we gather and use intelligence".
Neither Carney or Obama have commented on specific allegations that the U.S. eavesdropped on international allies, including tapping the phones of foreign officials.
German media reported that the U.S. had bugged German Chancellor Angela Merkel's phone for more than a decade - and that the surveillance only ended a few months ago.
Jay Carney: "There has been extraordinary change... in the way we transmit and gather information"
An across-the-board review of U.S. intelligence resources is currently under way.
The head of the NSA, Gen Keith Alexander, and other experts are due to testify before the House of Representatives intelligence committee at 13:30 local time (17:30 GMT) on Tuesday, October 29.
The BBC's Jonny Dymond in Washington says tough questions can be expected from Congress as politicians of all stripes have been angered by the revelations of large scale intelligence gathering on both Americans and U.S. allies.