US Secretary of State John Kerry said US spying has gone too far in some cases, an unprecedented admission by Washington in the row with Europe over widespread surveillance.
"The president and I have learned of some things that have been happening in many ways on an automatic pilot, because the technology is there and the ability is there," he told a conference in London via video link.
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The top diplomat also sought to assure that such steps, which have roiled close allies like Germany, would not be repeated.
"I assure you, innocent people are not being abused in this process, but there's an effort to try to gather information," Kerry told a London conference via video link. "And yes, in some cases, it has reached too far inappropriately."
"And the president, our president, is determined to try to clarify and make clear for people, and is now doing a thorough review in order that nobody will have the sense of abuse," he said.
Kerry added that what Washington was trying to do was, in a "random way," find ways of determining if there were threats that needed responding to.
"And in some cases, I acknowledge to you, as has the president, that some of these actions have reached too far, and we are going to make sure that does not happen in the future," he said.
Recent allegations and reports of widespread spying by the US National Security Agency have sparked a major rift in trans-Atlantic ties.
Just days ago, German Chancellor Angela Merkel angrily confronted President Barack Obama with allegations that the NSA was snooping on her phone, saying it would amount to a "breach of trust."
A German intelligence delegation and a separate group of EU lawmakers were in the US capital Wednesday to confront their American allies about the alleged bugging.
Kerry's remarks -- released in a State Department transcript -- came in response to a question addressed to both him and British Foreign Secretary William Hague about government surveillance.
Kerry spent a good portion of his answer justifying the collection of data as necessary due to the threat of terrorism and suggested Washington was not alone in doing so.
"Many, many, many parts of the world have been subject to these terrorist attacks," he said.
"And in response to them, the United States and others came together -- others, I emphasize to you -- and realized that we're dealing in a new world where people are willing to blow themselves up."
He added: "We have actually prevented airplanes from going down, buildings from being blown up, and people from being assassinated because we?ve been able to learn ahead of time of the plans."
Kerry also lashed out at some of the reporting about alleged spying, sparked by leaks from fugitive former NSA contractor Edward Snowden, wanted by Washington on espionage charges.
"Just the other day... there was news in the papers of 70 million people being listened to. No, they weren't. It didn't happen," Kerry said.
"There's an enormous amount of exaggeration in this reporting from some reporters out there."
US intelligence chiefs have said these reports are based on a misinterpretation of an NSA slide leaked to the media by Snowden.
Rather than siphoning off the records of tens of millions of calls in Europe, as the slide seems to suggest, they argue that the data was in many cases gathered and shared by European agencies.
Still, fresh US spy allegations keep cropping around the world on a near daily basis.
Indonesia summoned the Australian ambassador in Jakarta Friday over a "totally unacceptable" report that his embassy was among diplomatic posts in Asia being used in a vast American surveillance operation.
The Sydney Morning Herald newspaper, amplifying an earlier report by the German magazine Der Spiegel, said earlier this week that a top-secret map leaked by Snowden showed 90 US surveillance facilities at diplomatic missions worldwide.
The paper also reported that Australian embassies in Asia were being used as part of the US-led spying network.
On Wednesday, meanwhile, a report in the Washington Post alleged that NSA technicians had tapped into Yahoo and Google data centers around the world, winning access to vast amounts of private data.
The report said a program dubbed MUSCULAR, operated with the NSA's British counterpart GCHQ, can intercept data directly from the fiber-optic cables used by the US Internet giants.
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