In the second chat, which is understood to have been created by Mr Hegseth himself on his personal phone, the cabinet member allegedly posted details of the flight schedules of the F/A-18 air strikes against the Iran-backed group in Yemen.

Mr Hegseth’s wife Jennifer, a former Fox News producer, has previously been criticised for reportedly attending sensitive meetings with foreign military counterparts, according to the Wall Street Journal.

The move invited further questions about national security and top US officials using unclassified messaging apps to share sensitive information.

Meanwhile, NPR reported the White House had “begun the process of looking for a new” defence secretary, citing a US official who “was not authorised to speak publicly”.

‘Fake news’

Karoline Leavitt, Mr Trump’s press secretary, who earlier insisted Mr Hegseth had the White House’s full backing, branded the story “fake news”.

“This ⁦@NPR⁩ story is total FAKE NEWS based on one anonymous source who clearly has no idea what they are talking about,” she wrote on X. “As the president said this morning, he stands strongly behind ⁦@SecDef⁩.”

The second Signal chat, which was named “Defense Team Huddle” included around a dozen people and was reportedly created before Mr Hegseth was confirmed as defence secretary.

Mr Hegseth reportedly posted details of the strikes in both chats at around the same time.

A source told The New York Times that Mr Hegseth’s aides had urged him not to discuss sensitive operations in his Signal group chat days before the strikes.

While Mr Hegseth’s brother Phil and Tim Parlatore, his lawyer, both have jobs in the Pentagon, it is not clear why they would be informed about the planned strikes.

The Signal chat reportedly included Dan Caldwell, one of Mr Hegseth’s leading advisers, who was escorted from the Pentagon last week after being identified during an investigation into leaks at the department of defence, according to officials.

Following Mr Caldwell’s departure, less senior officials Darin Selnick, who recently became Mr Hegseth’s deputy chief of staff, and Colin Carroll were put on administrative leave, pending an investigation, the Pentagon confirmed.

Mr Caldwell, Mr Selnick and Mr Carroll have denied leaking. In a joint statement on Saturday they said: “Unnamed Pentagon officials have slandered our character with baseless attacks on our way out the door.

“We still have not been told what exactly we were investigated for, if there is still an active investigation, or if there was even a real investigation of ‘leaks’ to begin with.”

‘Pentagon in disarray’

Elsewhere, in a bombshell op-ed for Politico, John Ullyot, who resigned from the Pentagon, said it is in “total chaos” and that Mr Hegseth was unlikely to remain in his role.

“The building is in disarray under Hegseth’s leadership,” Mr Ullyot wrote on Sunday.

“The dysfunction is now a major distraction for the president — who deserves better from his senior leadership.”

Mr Hegseth told reporters at the White House Easter Egg roll on Monday: “[The media] take anonymous sources from disgruntled former employees, and then they try to slash and burn people and ruin their reputations. Not going to work with me.”

“I have spoken to the president, and we are going to continue fighting, on the same page all the way,” he added.

The president offered his full support to Mr Hegseth in a phone call on Saturday, the New York Times reported.