The US justice department has “tripled the number of active leak investigations” and devoted new FBI resources to cracking down on leakers, Jeff Sessions, the attorney general, said in a press conference on Friday, promising also that the department was reviewing its approach to subpoenaing journalists.

“We respect the important role that the press plays and will give them respect, but it is not unlimited. They cannot place lives at risk with impunity,” Sessions warned. “We must balance their role with protecting our national security and the lives of those who serve in our intelligence community, the armed forces, and all law abiding Americans.”

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Sessions condemned the “staggering number of leaks” and said that in the first six months of the Trump administration, the department had already received “nearly as many criminal referrals” involving disclosure of classified information as it had received in the last three years combined.

“I have this message for the intelligence community: the Department of Justice is open for business,” Sessions said. “And I have this warning for would-be leakers: don’t do it.”

After a week of criticism of the attorney general from Donald Trump, who tweeted in late July that Sessions “has taken a VERY weak position...on INTEL leakers!” the press conference served as a public message to the president that he is following Trump’s wishes.

Sessions’ announcement was heavy on threats and light on specifics. As the attorney general noted, the department’s practice is not to comment on active investigations.

Sessions did highlight one potential policy change: following months of attacks by the president on the press for publishing leaked information from the highest levels of his administration, Sessions said the department was reviewing its policy on subpoenaing journalists.

After years of denunciations from news organizations over its own crackdowns on the press, which included secretly subpoenaing months of telephone records of Associated Press reporters and editors, Obama’s justice department announced in 2015 that it was increasing oversight of prosecutors’ choices to obtain records and other information from journalists when pursuing leak investigations.

Trump has spent months denouncing the “fake news” media and attacking the press, including individual journalists. The anti-media chants that were a staple of his campaign rallies have continued into the rallies Trump has held as president. News organizations have raised concerns about the broader effects of this undermining of press freedom, particularly after a Republican congressional candidate in Montana slammed Guardian reporter Ben Jacobs to the ground in May. Greg Gianforte, who won the race despite the assault on the eve of the election, later apologized, pleaded guilty to misdemeanor assault and was sentenced to community service.

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But Sessions’ promise to revisit how journalists will be treated represents a new kind of threat, one that journalists greeted with concern and, in some cases, defiance.

“The guidelines in place carefully balance the interests of both law enforcement and the news media. We strongly oppose DoJ plan to revisit,” the Reporters Committee for Freedom of the Press tweeted.

Trump’s week-long series of public attacks on his attorney general appear to have paused, at least for now. Bloomberg reported that Trump’s new chief of staff John Kelly reassured Sessions in a phone call over the weekend that he would keep his job.

Republicans in Congress had pushed back against the president’s attacks on Sessions, with one influential Republican tweeting bluntly that the Senate would not be holding confirmation hearings for a new attorney general this year. “No way,” Senator Chuck Grassley tweeted.

Sessions defended himself in a Fox News interview last week, saying that the president’s attacks were “kind of hurtful” but that he was effectively carrying out the president’s agenda.

“The president has every right to ask the Department of Justice to be more aggressive in that and we intend to,” Sessions told Tucker Carlson, promising “people need to go to jail.”

Sessions’ press conference came a day after it was reported that special counsel Robert Mueller has empanelled a grand jury in his investigation of links between Trump aides and Russia.

Key Trump aide Kellyanne Conway seemed to confirm the existence of the investigative panel on Friday, telling Fox News: “Remember, grand jury investigations are meant to remain secret. So someone leaked it.

“It could been anybody in the grand jury. It could be one of the lawyers. It could be anyone, I suppose. But what really should concern everyone, are these leaks that imperil national security.”

Most observers agreed that the existence of a grand jury would be bad news for the president, who could with his aides be subpoenaed to testify before it under oath. Bill Clinton testified to a grand jury over the Monica Lewinsky affair; Richard Nixon did so over Watergate.

The Wall Street Journal first reported that Mueller had convened the grand jury in Washington, a sign that investigators are intensifying their work on potential collusion between Trump aides and Moscow.

Subsequent reports suggested the grand jury had already subpoenaed documents in relation to the now infamous June 2016 meeting between Donald Trump Jr and a Russian lawyer, Natalia Veselnitskaya. The meeting, at Trump Tower in Manhattan, also included among others the president’s son-in-law and senior adviser Jared Kushner, then-campaign manager Paul Manafort, and a former Soviet counter-intelligence officer.

The meeting was revealed last month, forcing Trump Jr to make public emails in which he accepted the meeting on the premise of receiving highly sensitive information about Hillary Clinton, his father’s election rival. In the emails, the first public indication Trump aides might have been willing to conspire with Russians, Trump Jr was also explicitly told of an effort by the Kremlin to aid his father’s campaign.

The president, who has long refused to acknowledge the conclusion of US intelligence agencies that Moscow sought to influence the election, continues to cast the entire investigation as an attempt to delegitimize his victory over Clinton.

“Have you seen any Russians in West Virginia, or Ohio, or Pennsylvania?” Trump asked his audience on Thursday. “They can’t beat us at the voting booths so they’re trying to cheat you out of the future and the future that you want.

“They’re trying to cheat you out of the leadership that you want with a fake story that is demeaning to all of us, and, most importantly, demeaning to our country and demeaning to our constitution.”

The president’s legal team has reportedly looked into potential conflicts of interest involving Mueller and his team of investigators. In a recent New York Times interview, the president suggested he would soon make such matters public.

Ty Cobb, special counsel to the president, said on Thursday he was unaware of a grand jury. But he took a more congenial approach to the subject than his client.

“Grand jury matters are typically secret,” Cobb said. “The White House favors anything that accelerates the conclusion of his work fairly. The White House is committed to fully cooperating with Mr Mueller.”

Trump has been publicly critical of Mueller, who was appointed after the president fired FBI director James Comey in relation to the Russia investigation

Trump’s hostile approach to the Russia investigation has sparked growing concern on Capitol Hill. On Thursday, two bipartisan groups of senators unveiled legislation that would protect Mueller from being fired by the president.