US Secretary of State John Kerry has said that in some cases, US spying has gone too far.
Mr Kerry is the most senior Obama administration official to have commented directly on an issue that has upset America's European allies.
He said he will work with the president to prevent further inappropriate acts by the National Security Agency.
His comments come as Asian countries have protested at claims that Australia was involved in a US-led spy network.
China has demanded an explanation of the reports, while Indonesia has summoned the Australian ambassador to Jakarta.
In other developments:
- Major technology companies including Google, Apple and Yahoo have called for the US government to do more to rein in the NSA's activities.
- A German MP said ex-US intelligence contractor Edward Snowden is willing to travel to Berlin to help investigations into the alleged surveillance of Angela Merkel's phone.
- Indonesia's foreign minister said reports that the NSA used Australian embassies to eavesdrop on Asian countries would indicate a "serious breach" of diplomatic rules.
In his comments, Mr Kerry also defended the need for increased surveillance, saying it had thwarted terrorist attacks.
"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," Mr Kerry told a conference in London via video link.
"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.
"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... we are going to make sure that does not happen in the future." he said.
Mr Kerry, in his remarks to a conference organised by the Open Government Partnership, said that while some surveillance may have been excessive, claims that up to 70 million were being monitored were an "exaggeration".
Claims about the extent of US surveillance of targets such as European leaders have strained Washington's diplomatic relations with some of its key allies.
'Serious breach'
Last week it was alleged that German Chancellor Angela Merkel's mobile phone had been tapped for up to 10 years.
More recently there have been claims that the NSA hacked links connecting data centres operated by Google and Yahoo.
According to the Sydney Morning Herald, Australia embassies in Asia had been used to spy on Asian countries such as China, Indonesia, Singapore, Thailand and Vietnam.
"If confirmed, such action is not only a breach of security, but also a serious breach of diplomatic norms and ethics," Indonesian Foreign Minister Marty Natalegawa said.
The report describes a signals intelligence programme called Stateroom which involves the interception of radio, telecommunications and internet traffic using equipment in US, British, Australian and Canadian diplomatic missions.
Australia's Department of Foreign Affairs and Trade declined to comment on the latest reports.
Prime Minister Tony Abbott said: "Every Australian governmental agency, every Australian official... operates in accordance with the law."
The claims are the latest to emerge from documents leaked by ex-US intelligence contractor Edward Snowden, who has been granted temporary asylum in Russia and is wanted in the US in connection with the unauthorised disclosures.
Technology firms appeal
In Germany, a member of parliament has said Mr Snowden is willing to travel to Berlin to help investigate allegations about the tapping of Mrs Merkel's phone.
Hans-Christian Stroebele, who represents the opposition Green party, said there would need to be safeguards against Mr Snowden, who he recently visited in Moscow, being deported to the United States.
The BBC's Steve Evans, in Berlin, said Germany's Christian-Democrat-led government may be unwilling to invite Mr Snowden to the country, particularly as his presence would raise issues over extradition agreements with the United States.
In the wake of the claims about surveillance of online data centres, six major technology companies have called for the US government to do more to control the NSA's activities.
The six called for "appropriate oversight and accountability" in a letter sent to a US Senate committee sponsoring a bill designed to rein in the NSA.
AOL, Apple, Facebook, Google, Microsoft and Yahoo signed the letter to the Senate Committee on the Judiciary, saying the greater control would help to rebuild trust in government surveillance programs.
