US Attorney General Jeff Sessions said on Friday the Justice Department had tripled the number of investigations into unauthorised leaks of classified information and that four people had already been charged.
"We are taking a stand," Sessions told reporters as he announced the administration's efforts to battle what he called "the staggering number of leaks undermining the ability of our government to protect this country."
"This culture of leaking must stop," he said.
He announced the establishment of a special task force to investigate leaks.
He referred to the leaking of President Donald Trump's telephone conversation with his Mexican counterpart President Enrique Peña Nieto.
"Just yesterday, we saw reports in the media about conversations the president had with foreign leaders. No-one is entitled to surreptitiously fight to advance battles in the media by revealing sensitive government information. No government can be effective when its leaders cannot discuss sensitive matters in confidence or talk freely in confidence with foreign leaders."
It emerged in news reports from leaked transcripts of a conversation that Trump had with Nieto in January, that Trump had urged him not to openly publicly criticise Trump's campaign promise to build a wall on the US border with Mexico. During campaigning, Trump had promised to make Mexico pay for the wall.
Sessions went further to state that referrals for investigation to the Justice Department of leaks of classified information "had exploded." He said that in the first six months of the Trump administration, the department had received the same number of criminal referrals as had been received in the previous three years combined.
He said that investigations were underway and that four people had been charged for disclosing classified material. He said that the number of investigations underway was treble that at the end of last year.
Sessions did not immediately give the identities of the four people charged, but said they had been charged with unlawfully disclosing classified information or concealing contacts with foreign intelligence officers.
"I have this warning for would-be leakers: Don't do it!"
He said that the department would not hesitate to bring charges and the Federal Bureau of Investigation had established a special counter-intelligence unit to investigate leaks.
Sessions also had a go at the media and said that their access to information was not unfettered, especially when it came to classified information.
"We respect the important role that the media plays and we will give them respect. But it is not unlimited. They cannot place lives at risk with impunity. We must balance the press's role with protecting our national security and the lives of those who serve in the intelligence community, the armed forces and all Americans."
Trump has repeatedly voiced anger over a steady stream of leaks to the media about him and his administration since he took office in January. Some have been related to probes into Russian meddling in the 2016 U.S. presidential election, others have concerned infighting in the White House.
Speaking to reporters after the media event with Sessions, Deputy Attorney General Rod Rosenstein said the department was just starting to review the policy on media subpoenas and could not say yet how it might be changed. But he did not rule out the possibility of threatening journalists with jail time.
Under U.S. law, a government attorney must seek the attorney general's approval before issuing a subpoena to attempt to force a member of the news media to divulge information to authorities.