US Secretary of State John Kerry has conceded that US surveillance went "too far", after some of its closest allies complained about surveillance by the National Security Agency.
But Mr Kerry defended US intellgence efforts, which he said "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".
He 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."
He said President Barack Obama is leading "a thorough review" to ensure that the people's perception of abuse "does not happen in the future".