"Joe Kasper will continue to serve President Trump as a Special Government Employee (SGE) handling special projects at the Department of Defense," the official said, adding: "Secretary Hegseth is thankful for his continued leadership and work to advance the America First agenda."

His departure is the latest in a series of high-profile exits from top Pentagon posts, including three officials who were removed last week amid an investigation into leaks after they reportedly clashed with Kasper.

Former senior advisors Darin Selnick, Dan Caldwell and Colin Carroll hit back on Sunday, saying Pentagon officials had "slandered our character with baseless attacks."

"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," they said in a joint statement posted on social media.

Hegseth's former Pentagon press secretary John Ullyot also took aim at him in a scathing opinion piece on Sunday that described "a month of total chaos at the Pentagon."

"President Donald Trump has a strong record of holding his top officials to account. Given that, it's hard to see Defense Secretary Pete Hegseth remaining in his role for much longer," wrote Ullyot.

The shakeups come as Hegseth faces a new scandal over his reported use of messaging app Signal to discuss US strikes on Yemen with his wife and other people not usually involved in such discussions.

The White House has stood by him so far, just weeks after it emerged that Hegseth also shared details about the strikes against Yemen's Huthi rebels in another Signal chat to which a journalist had been inadvertently added.