One of US Defence Secretary Pete Hegseth’s top advisers has been placed on administrative leave, Fox News reported Tuesday.

Citing a Defence Department official, the report said Dan Caldwell was put on leave for an “unauthorised disclosure” of information. Caldwell previously argued that the US should dramatically reduce its footprint in Europe and pullout forces in Iraq and Syria, according to Fox News.

On March 21, Department of Defence Chief of Staff Joe Kasper signed a memo requesting a probe into “recent unauthorised disclosures of national security information involving sensitive communications.” “The use of polygraphs in the execution of this investigation will be in accordance with applicable law and policy,” Kasper wrote in the memo, adding the investigation will “commence immediately and culminate” in a report to Hegseth.

Separately, Fox News reported that Darin Selnick, Hegseth’s deputy chief of staff, was also placed on leave Tuesday. Both Caldwell and Selnick are under investigation for an alleged unauthorised disclosure of sensitive information.

The two officials, both formerly affiliated with Concerned Veterans for America—a group once led by Hegseth—are now being scrutinised as part of a broader probe announced in March.

Selnick, a retired Air Force officer who has worked extensively at veterans’ affairs organisations, was escorted from the building Tuesday, the report said. There is currently no confirmed link between either official and the alleged leak.