WASHINGTON — Dan Caldwell, a senior adviser to Defense Secretary Pete Hegseth, has been placed on administrative leave and was escorted out of the Pentagon by security on Tuesday, two defense officials said.

The officials said Caldwell’s sudden downfall was tied to an ongoing investigation into unauthorized disclosure of department information. The officials spoke on condition of anonymity to discuss personnel matters.

Caldwell, who served in the Marine Corps, was one of several senior advisers who worked closely with Hegseth. Caldwell’s ties to the secretary go back to Hegseth’s time as the head of Concerned Veterans for America, a nonprofit that fell into financial difficulty during his time there. Caldwell worked at CVA beginning in 2013 as policy director and later as executive director.

Caldwell’s ouster was first reported by Reuters.

The officials did not disclose what leaks are being investigated, but there has been a crackdown across the Pentagon and the Trump administration on the disclosure of sensitive or classified information.

On March 22, Hegseth’s chief of staff, Joe Kasper, said in a memo that the Pentagon was investigating what it said were leaks of national security information. Defense Department personnel could face polygraphs.

The memo referred to “recent unauthorized disclosures” but provided no details. Kasper warned that the investigation would begin immediately and result in a report to Hegseth.

“I expect to be informed immediately if this effort results in information identifying a party responsible for an unauthorized disclosure, and that such information will be referred to the appropriate criminal law enforcement entity for criminal prosecution,” Kasper said in the memo.

Caldwell, who graduated from Arizona State in 2011, also worked as a public policy adviser at Defense Priorities. a think tank based in Washington.