The National Security Agency intercepted Americans' e-mails and phone calls in recent months on a scale that went beyond limits set by Congress last year, The New York Times reported on Wednesday.
The problems were discovered during a review of the intelligence activities, the Justice Department said in a statement Wednesday night, and said they had been resolved.
Citing unnamed intelligence officials, the Times said the NSA had engaged in "'over-collection' of domestic communications of Americans." Sources reportedly described the practice as varying from significant to systemic to unintentional.
The agency also tried to wiretap a member of Congress without a warrant, an intelligence official told the Times.
The NSA believed that the congressman, whose identity was not revealed, was in contact with an extremist who had possible ties to terror and was already under surveillance. The NSA then tried to eavesdrop on the congressman's conversations, the Times said.
Director of National Intelligence Dennis C. Blair admitted Thursday that the NSA made mistakes and intercepted the wrong communications. But he emphasized the number of errors is small to the overall collection efforts and that each error is investigated, leading to corrective measures to prevent reoccurrences.
"Let me be clear. I do not and will not support any surveillance activities that circumvent established processes for their lawful authorization and execution," he said in a statement. "Additionally, we go to great lengths to ensure that the privacy and civil liberties of U.S. persons are protected."
Senate Intelligence Committee Chairman Dianne Feinstein said Thursday she will investigate the indications of new wiretap violations.
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.
In its statement, the Justice Department said it has taken "comprehensive steps to correct the situation and bring the program into compliance."
"As the Justice Department and National Security Agency were conducting routine oversight of intelligence activities to ensure compliance with existing laws and court orders, officials detected issues that raised concerns. Once these issues were identified, the Justice Department immediately notified the Foreign Intelligence Surveillance Court," said DOJ spokesman Dean Boyd, though he did not elaborate on what problems were found.
Once corrective measures were taken, Attorney General Eric Holder sought authorization for renewing the surveillance program, officials said.
"It is not clear to what extent the agency may have actively listened in on conversations or read e-mails of Americans without proper court authority, rather than simply obtain access to them," the Times said.
Domestic eavesdropping has been a contentious issue since 2005, when the Times revealed that for years following the Sept. 11, 2001, terrorist attacks, the NSA intercepted international phone conversations and e-mails involving U.S. citizens without a warrant.
That program ended in 2007, and the following year Congress passed legislation requiring the NSA to get court approval to monitor the purely domestic communications of Americans who came under suspicion.
The Associated Press contributed to this report.