A memo late Friday from Defence Secretary Pete Hegseth's chief of staff referred to "recent unauthorised disclosures" of such information but provided no details about alleged leaks.
Earlier in the day, President Donald Trump rejected reports that adviser Elon Musk would be briefed on how the United States would fight a hypothetical war with China.
"If this effort results in information identifying a party responsible for an unauthorised disclosure," then such information "will be referred to the appropriate criminal entity for criminal prosecution," according to the memo.
At the Homeland Security Department, Secretary Kristi Noem pledged this month to step up lie detector tests on employees to identify those who may be leaking information about operations to the media.
The Justice Department on Friday announced an investigation into "the selective leak of inaccurate, but nevertheless classified, information" from intelligence agencies about Tren de Aragua, a Venezuelan gang whose members in the United States are being targeted for removal by the Republican administration.
Leaks occur in every administration — and government officials can be the source — as a trial balloon to test how a potential policy decision will be received.
While polygraph exams are typically not admissible in court proceedings, they are frequently used by federal law enforcement agencies and for national security clearances.
In 1998, the Supreme Court ruled they were also inadmissible in military justice proceedings.
They are inadmissible because they are unreliable and often result in false positives, said George Maschke, a former Army interrogator and reserve intelligence officer who went on to found AntiPolygraph.org.
Mashke failed a polygraph himself when applying to the FBI.
But they have been intermittently used since the 1990s to intimidate and scare sources from talking to reporters, Maschke said.
A 1999 Pentagon report said it was expanding the program to use polygraphs on defence personnel: "if classified information they had access to has been leaked".
