The National Security Agency can keep copies of intercepted communications from or about U.S. citizens if the material contains significant intelligence or evidence of crimes.

That’s according to exemptions in NSA’s top secret rules published Thursday in the latest leak of classified U.S. materials.

Top secret documents published by The Guardian describe how NSA must first build a case in order to target a foreigner for phone or Internet surveillance. The documents also describe how the agency is to make sure the person is outside the U.S. — and not an American.

But if the target is communicating with an American, the record of contact can be kept indefinitely. Administration officials have said material NSA inadvertently gathers on Americans is destroyed. NSA did not immediately respond to requests for comment.

(AP)