Washington (CNN) Newly released "hazard reports" detailing encounters between US Navy aircraft and "unidentified aerial phenomena" reveal details about incidents that were thrust into the spotlight when the Pentagon officially declassified and released videos of three encounters late last month.

"The unknown aircraft appeared to be small in size, approximately the size of a suitcase, and silver in color," one report describing an incident from March 26, 2014, said.

During that encounter one of the Navy F/A-18 jets "passed within 1000' of the object, but was unable to positively determine the identity of the aircraft," the report added, saying the US Navy pilot "attempted to regain visual contact with the aircraft, but was unable."

CNN on Wednesday obtained the Navy Safety Center documents, which were previously labeled "For Official Use Only." They follow the Pentagon's official release late last month of three short videos showing "unidentified aerial phenomena" that had previously been made public by a private company.

The reports were first published by the Drive, a website covering auto news and military issues, which obtained the documents through a Freedom of Information Act request.

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