The US National Security Agency (NSA) admitted on Friday that the analysts had intentionally abused their spying power on Americans, which contradicts the Obama administration officials and lawmakers' assertion that no such violations occurred.

In a statement to US media, the NSA acknowledged "very rare instances of willful violations of NSA's authorities have been found" over the past decade.

"NSA takes very seriously allegations of misconduct, and cooperates fully with any investigations--responding as appropriate. NSA has zero tolerance for willful violations of the agency's authorities," the agency added.

According to Bloomberg News, which first reported the NSA's statement, one official said those violations were result of "over zealous NSA employees or contractors eager to prevent any encore to the Sept. 11, 2001, terrorist attacks."

The agency said the deliberate actions did not violate the 1978 Foreign Intelligence Surveillance Act or the USA Patriot Act, but instead overstepped a 1981 Executive Order governing US intelligence operations issued by President Ronald Reagan.

The agency's admission contradicts previous statements made by the Obama administration officials and lawmakers that the agency's violations of spying restrictions on Americans were only unintentional.

The White House spokesman Josh Earnest reiterated President Barack Obama's assertion on Wednesday that there is no domestic surveillance program going on in the country.

Earnest stressed that the NSA's surveillance efforts was focused on foreign intelligence and domestic information was only occasionally accessed by the agency as "compliance issues" rather than systematic spying on US citizens.

Last week, Senate Intelligence Committee Chairwoman Dianne Feinstein also said the committee had never identified an instance of the agency's deliberate abuse of spying power.

According to special court opinions declassified earlier this week, the NSA had improperly collected 56,000 emails and other communications between Americans annually for three years before the court ruled it unconstitutional. But the agency insisted that the collection was unintentional and only the result of failing to filter out domestic communications effectively in the program targeting foreign intelligence.