However, the probe by the inspector general's office concluded that Hegseth did not violate rules on classification because he has the authority to declassify information, the reports said, citing sources familiar with results of the investigation.

The watchdog's conclusion -- which has been transmitted to Congress -- is nonetheless likely to reignite debate over conduct by Hegseth, who is already under fire over US strikes on alleged drug-trafficking boats that experts say amount to extrajudicial killings.

The probe was sparked by the Atlantic magazine's revelation in late March that its editor-in-chief Jeffrey Goldberg was inadvertently included in a Signal chat in which US officials, including Hegseth and then-national security advisor Mike Waltz, discussed strikes on Yemen's Iran-backed Huthi rebels.

The chat included messages in which Hegseth revealed the timing of strikes hours before they happened and information on aircraft and missiles involved, while Waltz sent real-time intelligence on the aftermath of the military action.

The United States first began conducting strikes against the Huthis during the Biden administration in response to the rebels' attacks on shipping, and US forces launched a renewed air campaign against them on March 15.

Trump's strikes against the Huthis lasted until early May, when a ceasefire agreement was reached with the help of Omani mediation.