The Pentagon has placed two senior US Department of Defense officials on administrative leave as part of an investigation into "unauthorised leaks". Dan Caldwell, one of US Defense Secretary Pete Hegseth's leading advisers, and Darin Selnick, the Pentagon’s deputy chief of staff, were escorted from The Pentagon and had their building access suspended.

Caldwell, a Marine Corps veteran, has played a critical role as an adviser to Hegseth​. His importance was underscored ​"Signal-gate", the leaked text chain on Signal disclosed by The Atlantic last month​, in which Hegseth named Caldwell as the best staff point of contact for the National Security Council as it prepared for the launch of strikes against the Houthis in Yemen.

Caldwell, who previously worked at the right-leaning Defense Priorities think tank, played a key role in advising the Pentagon on Ukraine and holds isolationist views.

He was a sceptic of US military assistance to Ukraine and advocated for US retrenchment from Europe.

The Iraq veteran last year he was quoted as saying that America would have been better off if US troops had just stayed home.

"I think the Iraq war was a monstrous crime," he said publicly in December.

Selnick, also performed the duties of the under secretary of Defense for personnel and readiness. He served in the White House and the Department of Veterans Affairs in the first Trump administration.

Both men also previously worked for Concerned Veterans for America, which Hegseth used to lead.

A March 21 memo signed by Hegseth's chief of staff, Joe Kasper, requested an investigation into "recent unauthorised disclosures of national security information involving sensitive communications."

Kasper's memo left open the possibility of a polygraph, although it was unclear if Caldwell was subjected to one.

Other leaks under investigation include military operational plans for the Panama canal, a second carrier headed to the Red Sea, Elon Musk’s controversial visit to the Pentagon and pausing the collection of intelligence to Ukraine.

Sources told Reuters that ”the investigation remains ongoing."