An internal audit said the NSA broke privacy rules protecting communications on U.S. soil 2,776 times in one year and "thousands of times each year since 2008," The Washington Post reported Friday.
"I will continue to demand honest and forthright answers from the intelligence community," Sen. Leahy, D-Vt., chairman of the Senate Judiciary Committee said Friday, adding his committee will hold another hearing on the Post's revelations.
The audit, leaked to the newspaper by former NSA contractor Edward Snowden earlier this summer, cited 2,776 incidents in the previous 12 months of unauthorized gathering, storage, contact or sharing of legally protected communications, the newspaper said.
The most serious incidents in the 12 months included a defiance of a court order and unauthorized use of data of about more than 3,000 U.S. citizens and green-card holders, said the Post, which accompanied its article with some of the documents it cited.
The infractions range from significant law violations to typographical errors that resulted in accidental interception of U.S. emails and phone calls.
One document indicated agency personnel were told to replace specific surveillance details with generic language in reports to the Justice Department and the Office of the Director of National Intelligence, the Post said.
The NSA told the Post in a statement it tries to identify problems "at the earliest possible moment, implement mitigation measures wherever possible, and drive the numbers down."
"We're a human-run agency operating in a complex environment with a number of different regulatory regimes, so at times we find ourselves on the wrong side of the line," a senior NSA official told the Post, speaking anonymously with White House permission.
"You can look at it as a percentage of our total activity that occurs each day," he said. "You look at a number in absolute terms that looks big, and when you look at it in relative terms, it looks a little different."
Another NSA statement, released Thursday, said its activities are "continually audited and overseen, internally and externally. When NSA makes a mistake in carrying out its foreign intelligence mission, the agency reports the issue internally and to federal overseers, and aggressively gets to the bottom of it."