Marc Piscotty / Getty Images file Najibullah Zazi, seen in 2009 image, was accused of plotting to bomb New York City's subway system.

U.S. intelligence officials said Saturday that National Security Agency surveillance programs have disrupted "dozens" of terrorist plots in the U.S. and more than 20 countries around the world.

The statement about the thwarted plots was cleared for release by U.S. officials late Saturday afternoon after requests by Senate Intelligence Committee chair Sen. Dianne Feinstein that intelligence agency officials release more information about the surveillance programs to show their effectiveness.

In the statement, intelligence officials said that, of the hundreds of millions of records of U.S. phone calls collected under a provision of the Patriot Act, only 300 were "queried" in 2012 for additional information about the callers.

This was done only after officials found there was a "reasonable suspicion" that the person making the call was "associated with specific foreign terrorist organizations," according to a statement cleared for release by U.S. intelligence agencies.

The only example cited of a thwarted terrorism plot was what officials described as a " major Al-Qa'ida directed attack" intended for the U.S. homeland in 2009. After the NSA discovered that al Qaeda terrorists in Pakistan were in contact with an "unknown person" in the U.S. , the agency alerted the FBI, the intelligence community statement said. The bureau then identified the U.S. contact as Colorado-based extremist Najibullah Zazi.

After getting Zazi's U.S. phone number from the FBI, the NSA ran it against its mass database of U.S phone calls and discovered a "previously unknown" number for a Zazi co-conspirator, Adis Medunjanin.

The FBI then tracked Zazi as he traveled to New York and arrested him. He pleaded guilty in 2010 to a bomb plot aimed at the New York City subway system and was sentenced to life in prison. Medunjanin was also arrested, convicted and sentenced to life in prison. Officials described the plot "as the most serious terrorist threat on US soil since 9/11," according to the intelligence community statement.

The "operational details" of other plots disrupted "must remain secret to allow us to continue to effectively leverage our capabilities in the face of those who still aspire to do great harm to our citizens and allies," the statement said.

The statement said that both the program for the collection of telephone metadata and a separate one that intercepts the content of phone calls and emails of foreigners suspected of terrorism operate under “strict controls” that protect the civil liberties of Americans. It emphasized that both are overseen and approved by the secret Foreign Intelligence Surveillance Court, or FISC.

It also revealed for the first time that records of phone calls that are collected must be destroyed within five years.

The statement made no reference to what critics have charged have been instances of improper interception of emails and phone calls, including an 86-page, Oct. 3, 2011, FISC opinion — the existence of which was disclosed in a recent Freedom of Information Act lawsuit — finding that some surveillance by the intelligence community was conducted under procedures that violated the Fourth Amendment to the Constitution prohibiting “unreasonable” searches and seizures by the government.

Feinstein's office said the senator would have no comment on the statement on Saturday.

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