Hegseth has denied the information he shared was classified, but it was given to him on a system for sensitive and classified information, sources told NBC News.

Minutes before U.S. fighter jets took off to begin strikes against Iranian-backed Houthi rebels in Yemen last month, Army Gen. Michael Erik Kurilla, who leads U.S. Central Command, used a secure U.S. government system to send detailed information about the operation to Defense Secretary Pete Hegseth.

The material Kurilla sent included details about when U.S. fighters would take off and when they would hit their targets — details that could, if they fell into the wrong hands, put the pilots of those fighters in grave danger. But he was doing exactly what he was supposed to: providing Hegseth, his superior, with information he needed to know and using a system specifically designed to safely transmit sensitive and classified information.

But then Hegseth used his personal phone to send some of the same information Kurilla had given him to at least two group text chats on the Signal messaging app, three U.S. officials with direct knowledge of the exchanges told NBC News.