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U.S. Director of National Intelligence James Clapper (right) and General Keith Alexander, director of the National Security Agency, testify at a House Intelligence Committee hearing on October 29. The head of US intelligence has told lawmakers that discerning foreign leaders' intentions is a key goal of the nation's spying operations.
Director of National Intelligence James Clapper said such efforts were a "top tenet" of US intelligence policy.
But he told the intelligence panel of the House of Representatives the US did not "indiscriminately" spy on nations.
Mr Clapper was reacting to a growing international row over reports the US eavesdropped on foreign allies.
"Leadership intentions is kind of a basic tenet of what we collect and analyse," Mr Clapper said, adding that foreign allies spy on US officials and intelligence agencies as a matter of routine.
He said that what he called the torrent of disclosures about American surveillance had been extremely damaging and that he anticipated more.
But he said there was no other country that had the magnitude of oversight that the US had, and that any mistakes that had been made were human or technical.
The BBC's Jonny Dymond in Washington says if anyone was expecting apologies or embarrassment from the leaders of America's intelligence community they were in for a disappointment.
Also testifying before the House intelligence committee was National Security Agency (NSA) director Gen Keith Alexander, who called media reports in France, Spain and Italy that the NSA gathered data on millions of telephone calls "completely false".
The information "that led people to believe that the NSA or United States collected that information is false, and it's false that it was collected on European citizens," he added. "It was neither."
Gen Alexander said much of the data cited by non-US news outlets was actually collected by European intelligence services and later shared with the NSA.
Gen Alexander added: "It is much more important for this country that we defend this nation and take the beatings than it is to give up a programme that would result in this nation being attacked."
Our correspondent says the intelligence pair were not given a tough time by the committee but that sentiment is turning within Congress toward tightening up the reach of American intelligence agencies.
The testimony came amid a series of reports in the international news media that the NSA had spied extensively on the leaders, diplomats and citizens of nations friendly to the US, including Brazil, France, Germany, Mexico and Spain.
The revelations stem from documents leaked by fugitive ex-US intelligence contractor Edward Snowden, who now lives in Russia and is wanted in the US in connection with the unauthorised disclosures.
President Barack Obama has faced significant criticism over reports he was unaware of the extent of the spying.
In a television interview, the US president said the country's national security operations were being reassessed to ensure the NSA's growing technological 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."
'Totally opposed'
In one of the most significant disclosures, German media have 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.
It has also been reported that the NSA spied on French diplomats in Washington and at the UN, and that it conducted surveillance on millions of French and Spanish telephone calls, among other operations against US allies.
On Monday, US Senate intelligence committee chairwoman Dianne Feinstein called for an end to eavesdropping on leaders of the nation's allies.
Ms Feinstein said the White House had told her such surveillance would stop, but a senior administration official told the BBC there was no policy change so far.
"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."