The US' surveillance programme "reached too far", a London audience has been told by John Kerry.
The US secretary of state conceded in a videolink to the Open Government Partnership conference that the revelations from whistleblower Edward Snowden had shown the American government was behaving inappropriately.
His admission comes amid international outrage at allegations that 35 world leaders were spied on, as well as claims that the National Security Agency monitored servers at nine internet companies, accessed 70 million records in France and spied on 35 embassies and missions.
"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," Kerry said.
"In some cases, some of these actions have reached too far and we are going to try to make sure it doesn't happen in the future."
He was quick to defend the US intelligence services for their efforts, however, arguing their motivation was clear.
"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 added.
"I assure you, innocent people are not being abused in this process, but there's an effort to try to gather information. And yes, in some cases, it has reached too far inappropriately."
He said president Barack Obama was conducting a "thorough review" which would ensure that the "sense of abuse" would not continue in the future.
The NSA's director, Keith Alexander, has rejected Obama and Kerry's claim that the intelligence agencies had got carried away.
"We the intelligence agencies don't come up with the requirements, the policymakers come up with the requirements," he said.
The latest claims centre around alleged Australian cooperation with the US in spying on Asian countries like China, Vietnam and Thailand.
Indonesian foreign minister Marty Natalegawa has suggested the US' actions, if confirmed, are a "serious breach of diplomatic norms and ethics".