The Senate’s intelligence committee has ordered a major review of the US surveillance operations.
The committee’s chair, Senator Dianne Feinstein, said eavesdropping on leaders of friendly nations was wrong.
Dianne Feinstein said the White House had told her such surveillance would stop.
Senior US intelligence agency officials are to testify before the House of Representatives later on Tuesday.
Correspondents say pressure is growing on the White House to explain why President Barack Obama apparently did not know about the extent of the intelligence gathering operations.
Barack Obama has spoken publicly of his intent to probe spying activities amid claims of eavesdropping on US allies.
In a recent interview, Barack Obama said that national security operations were being reassessed to make sure the NSA’s growing technical spying capability was kept under control.
“We give them policy direction,” Barack Obama told ABC’s Fusion channel.
“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.”
An EU delegate in Washington has described the row over intelligence gathering as “a breakdown of trust”.
German media has reported that the US bugged German Chancellor Angela Merkel’s phone for more than a decade – and that the surveillance only ended a few months ago.
Dianne Feinstein, who chairs the Senate intelligence panel, called for a “total review” of US intelligence programmes in light of the Merkel revelations.
“With respect to NSA collection of intelligence on leaders of US allies – including France, Spain, Mexico and Germany – let me state unequivocally: I am totally opposed,” she said in a statement.
“It is my understanding that President Obama was not aware Chancellor Merkel’s communications were being collected since 2002. That is a big problem.”
Dianne Feinstein said the White House had told her that all surveillance of leaders of countries friendly to the US would stop.
The US has had a “no spying pact”, known as Five Eyes, with Britain since just after World War II, with Australia, New Zealand and Canada later joining.
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