U.S. authorities gathered information about Huawei Technologies Co. Ltd. through secret surveillance they plan to use in their case charging the Chinese telecom company with violating sanctions against Iran, prosecutors said Thursday.

Assistant U.S. Attorney Alex Solomon said at a hearing in federal court in Brooklyn the evidence, obtained under the U.S. Foreign Intelligence Surveillance Act (FISA), would require classified handling. Information gathered under FISA is generally used in espionage cases.

The government notified Huawei in a court filing Thursday of its intent to use the information, saying it was "obtained or derived from electronic surveillance and physical search," but gave no details.