Responding to a question in a video-conference on open government in London, Kerry acknowledged that in some cases, the surveillance activities by the US spying agency National Security Agency (NSA) "have reached too far", Xinhua reported.
"There is no question that the president and I and others in government have actually learned of some things that had been happening, in many ways, on an automatic pilot because the technology is there," Kerry was quoted as saying.
The top US diplomat was apparently referring to the reports that the NSA had monitored the cell phones of 35 world leaders, including German chancellor Angela Merkel, and collected data on tens of millions of phone calls in European countries.
Kerry promised that "we are going to make sure that does not happen in the future".
However, Kerry defended the NSA's operations, citing the US surveillance as an "effective counter-terrorism tool" that had prevented terrorists from blowing up buildings, crashing airplanes and murdering people as the NSA was able to "learn ahead time of the plans".
The Obama Administration has come under increasing criticism and pressure from the international community since June after former NSA contractor Edward Snowden exposed its secret massive spying programmes which monitor worldwide phone calls and Internet communications under the excuse of counter-terrorism.
Washington has promised to conduct a review of its spying operations worldwide as part of its damage control efforts.