WASHINGTON — U.S. Defense Secretary Mark Esper has ordered an investigation into leaks of both classified and unclassified material to media, he told members of the House Armed Services Committee during a Thursday hearing.

The secretary brought up what he called an aggressive effort to pursue leaks after a series of what he called “bad leaks” in the fall.

“I’ve launched an investigation that is underway to go after leaks, whether it’s of classified information or unclassified information that is sensitive and also, you know, unauthorized discussions with the media,” Esper said. “All those things, again, hurt our nation’s security. They undermine our troops, their safety. They affect our relations with other countries. They undermine our national policy.

“The illegal leaks are terrible. They’re happening across the government, particularly in the Defense Department.”

He also said he is launching a new effort to “remind people” of operational security issues in the Pentagon.

Esper’s comments came after both he and Chairman of the Joint Chiefs of Staff Gen. Mark Milley reaffirmed in front of lawmakers their belief that a free and open press is vital to American democracy.

“I am deeply committed to a free press,” Milley said. “I will die for the Constitution. It is an idea, and part of that is a free media, and a free media is fundamentally essential to a free people, and it is fundamental to our democracy. So absolutely I’m committed to that.”

Said Mandy Smithberger, director of the Straus Military Reform Project at the Project on Government Oversight: “It’s hard to believe in Secretary Esper’s commitment to the First Amendment and the need for a free press when he simultaneously threatens to investigate those who see the need to raise concerns about wrongdoing.”

Esper’s comments are particularly concerning, Smithberger said, in light of the situation surrounding Lt. Col. Alexander Vindman, who claims he was pressured to retire from the military for his testimony during the impeachment of President Donald Trump, despite pledges from Pentagon leaders that there would be no retaliation.

If Esper is “committed to ending leaks, he should start with strengthening whistleblower protections,” Smithberger said.

“Fundamental principles of our democracy are transparency and accountability, and the department has backslid significantly when it comes to openness and responsiveness,” Smithberger added. Her group has called for a “public interest balancing test, so that we’re not wasting government resources on investigating or prosecuting disclosing information the public has a right to and needs to know.”

Several Republican lawmakers brought up the question of leaks during Thursday’s hearing, while questioning media reports, based on intelligence sources, that Russia had paid insurgents in Afghanistan to target American forces.

That context led Rep. Seth Moulton, D-Mass., a combat veteran, to note: “I don’t think you get to pick and choose which leaks you like, which leaks aren’t damaging versus what is an [operational security] problem. This White House routinely uses leaks to their advantage, but suddenly it’s a problem for their apologists.”

Esper would hardly be the first defense secretary to try to stop the flow of unauthorized information. It was a major focus for former Defense Secretary Jim Mattis in the first two years of the Trump administration, to the point that he implemented a crackdown on information sharing at the Pentagon. As a result, what was once routine information to be shared with the public became opaque over concerns of operational security.

One major issue for the media during Mattis’ tenure was getting information about what forces were being deployed and to where, with force numbers in Syria and Afghanistan particularly tough to nail down. It’s a policy that has continued, first under acting Defense Secretary Pat Shanahan and now Esper, who in January told reporters: “Gen. Mattis had a policy: We just don’t talk specific troop numbers, where we have, wherever they are. So I follow that.”

The question of troop numbers is being challenged through an amendment included in the HASC’s markup of the National Defense Authorization Act.