US Attorney-General Jeff Sessions has taken up an issue that has infuriated President Donald Trump, going on the attack against leaks and saying the Government was reviewing policies on compelling journalists to reveal sources.

Key points: Mr Sessions said policies on media subpoenas will be reviewed

Mr Sessions said policies on media subpoenas will be reviewed He said the number of investigations into unauthorised leaks has tripled

He said the number of investigations into unauthorised leaks has tripled A transcript of a phone call between Mr Trump and Malcolm Turnbull was leaked on Friday

In the latest high-profile leak to the media, the Washington Post on Friday published transcripts of phone calls that Mr Trump had with Prime Minister Malcolm Turnbull and Mexican President Enrique Pena Nieto.

Other leaks have been related to probes into Russian meddling in the 2016 US presidential election and infighting in the White House.

Mr Trump has repeatedly voiced anger over the steady stream of leaks to the media about him and his administration since he took office in January.

"No government can be effective when its leaders cannot discuss sensitive matters in confidence or to talk freely in confidence with foreign leaders," Mr Sessions said.

What does Trump have to say about the crackdown? Absolutely nothing today — he is headed off for a 17-day working holiday to his golf resort in New Jersey while the White House undergoes some renovations. But it has been something that has been a huge bugbear of his in the past. He tends to, whenever there's revelations of chaos in the White House, he attacks leakers, he attacks the press. It was something he hired Anthony Scaramucci — who had a brief tenure as communications director — specifically to try and crack down on. But one of the interesting things is Donald Trump is often the source of leaks himself. He is known to call journalists, to background them and brief them, and it is something he has done not just during his tenure as President, but during his entire public life. So there's sort of mixed messages coming out there, but it's likely that Jeff Sessions' move today, if effective, will go some way towards pleasing the President and possible provide some relief to the Attorney-General, who has proved a bit of a punching bag to Donald Trump in recent weeks. -Analysis by Washington correspondent Stephanie March

"One of the things we are doing is reviewing policies affecting media subpoenas," he told reporters as he announced efforts to battle what he called a "staggering number of leaks undermining the ability of our government to protect this country".

"We respect the important role that the press plays and will give them respect, but it is not unlimited."

A media subpoena is a writ compelling a journalist to testify or produce evidence, with a penalty for failure to do so.

The fact the administration is reviewing its policy leaves open the possibility of sentencing journalists for not disclosing their sources.

Speaking to reporters after the media event with Mr 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.

He did not rule out the possibility of threatening journalists with jail time.

Under US 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.

Investigations into leaks triple, four people charged

In addressing the wider issue of leaks, Mr Sessions said the Justice Department has tripled the number of investigations into unauthorised leaks of classified information and four people had already been charged.

Mr 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.

"We are taking a stand," Mr Sessions said.

"This culture of leaking must stop."

In recent weeks Mr Sessions has been publicly criticised by Mr Trump for his performance in the job, including for what the President called his weakness on the issue of going after leakers.

Mr Rosenstein would not say whether the crackdown on leaks came at the request of the White House, and did not give the exact number of investigations the Justice Department is currently handling, saying only that this number has tripled under the Trump administration.

Director of National Intelligence Dan Coats, who also attended the press conference, said leaks of classified information endangered national security.

He said such national security breaches came from a wide range of sources, including the executive branch and Congress.

Sorry, this video has expired John Barron talks about recent White House leaks

Reuters