The Pentagon’s independent watchdog said US Defence Secretary Pete Hegseth’s use of the commercial messaging app Signal to discuss strikes on Yemen could have put American troops at risk, US media reported on Wednesday.

The probe by the inspector general’s office concluded that Hegseth did not, however, violate rules on classification because he has the authority to declassify information, the reports said, citing sources familiar with the 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 was inadvertently included in a Signal chat in which US officials, including Hegseth and then-national security adviser Mike Waltz, discussed strikes on Yemen’s Iran-backed Huthi rebels.

The magazine initially withheld the details the officials discussed, but later published them after the White House insisted that no classified information was shared and attacked the editor, Jeffrey Goldberg, as a liar.

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.

In a post to X late on Wednesday, Pentagon spokesman Sean Parnell called the review “a TOTAL exoneration of Secretary Hegseth”.

Waltz fired, Hegseth survives

The Atlantic said that Waltz had set some of the Signal messages to disappear after one week, and others after four, saying it raised questions about whether federal records law was violated.

Trump rejected calls for Hegseth to be fired and largely pinned the blame on Waltz, whom he ultimately replaced as national security advisor, appointing him as US ambassador to the United Nations instead.

US media then reported in April that Hegseth had created a second Signal chat in which the March Yemen strikes were discussed with people, including his wife and brother, but the Pentagon chief likewise weathered that storm and remained in office.

The Houthis began targeting shipping in the Red Sea and Gulf of Aden after Israel’s offensive in Gaza began in 2023, claiming solidarity with Palestinians.

Houthi attacks prevented ships from passing through the Suez Canal, a vital route that normally carries about 12 per cent of world shipping traffic, forcing many companies into a costly detour around southern Africa.

The United States first began conducting strikes in response to the attacks under the Biden administration, and US forces launched a renewed air campaign against the Houthis on March 15.

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