The National Security Agency intercepted Americans' e-mails and phone calls in recent months on a scale that went beyond limits set by the U.S. Congress last year, The New York Times reported on Wednesday.
Citing unnamed intelligence officials, it said the NSA had engaged in "'over-collection' of domestic communications of Americans." The sources variously characterized the practice as significant, systemic or unintentional, the Times said.
"A series of classified government briefings have been held in recent weeks in response to a brewing controversy that some officials worry could damage the credibility of legitimate intelligence-gathering efforts," the paper said.
It said the Justice Department acknowledged in a statement on Wednesday that there had been problems with NSA surveillance operations and said they were resolved.
A bill passed by Congress in July 2008 authorizes U.S. intelligence agencies to eavesdrop without court approval on foreign targets believed to be outside the United States.
Critics complained that this allowed warrantless surveillance of phone calls and e-mails of Americans who communicate with the foreign targets. The bill sought to minimize such eavesdropping on Americans, but critics said the safeguards were inadequate.
The Times said "congressional investigators say they hope to determine if any violations of Americans' privacy occurred."