WASHINGTON - US Attorney General Jeff Sessions on Friday vowed a tough crackdown on people revealing classified or sensitive national security information, threatening to jail leakers and branding such illicit acts a betrayal to fellow Americans.

President Donald Trump has repeatedly fumed about "illegal leaks " and even lashed out publicly at Sessions last week for taking what he called a "very weak" position on the issue.

Under pressure, and with some saying his job could be on the line, Sessions responded. "I strongly agree with the president and condemn in the strongest terms the staggering number of leaks undermining the ability of our government to protect this country," Sessions told a press conference.

Four people have already been charged with "unlawfully disclosing" classified material or concealing contacts with federal officers, he said.

The number of active leak investigations this year has tripled compared with the tally before Trump took office, Sessions added. "We are taking a stand. This culture of leaking must stop," he said.

Director of National Intelligence Dan Coats, joining Sessions, issued his own tough warning to would-be leakers and described such revelations as "betraying" the American people.

"Understand this: If you improperly disclose classified information, we will find you," he said. "We will investigate you, we will prosecute you to the fullest extent of the law."

The announcement comes after six months of political intrigue and open feuding in the White House, which has manifested itself in a torrent of damaging revelations to the media.

It also follows a leak that was unusual even by the standards of this administration - the publication by The Washington Post of the contents of private phone calls between Trump and foreign leaders.

The newspaper published the full transcripts Thursday of conversations the Republican billionaire leader held in January with Mexican President Enrique Pena Nieto and Australian Prime Minister Malcolm Turnbull.

Sessions, while not addressing specifics of the transcripts, signalled his anger over the revelations which apparently came from inside the White House, saying "no government can be effective" when its leaders' discussions of sensitive matters are released.

The attorney general issued a not-so-veiled threat to the media, saying that while the administration has respect for the press, "it is not unlimited."

"They cannot place lives at risk with impunity," he added. "We must balance the press's role with protecting our national security."

 

Meanwhile, Donald Trump has described Russian interference in the 2016 presidential election as a "total fabrication" amid reports that a special prosecutor has empanelled a grand jury to investigate the issue - a step toward possible criminal indictments.

"We didn't win because of Russia. We won because of you," Trump said at a campaign-style rally in West Virginia.

Trying to build support among his core supporters, he said his enemies were "trying to cheat you out of the leadership 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 reason why Democrats only talk about the totally made-up Russia story is because they have no message, no agenda, and no vision," he said. "The Russia story is total fabrication. It's just an excuse for the greatest loss in the history of American politics."

His comments came after the Wall Street Journal revealed that special counsel Robert Mueller has empanelled a grand jury to investigate Russia's interference with the 2016 presidential election.

The newspaper, citing two unnamed sources familiar with the matter, reported that the grand jury had begun its work in the US capital Washington "in recent weeks."

The move is a sign that the sweeping federal investigation - which includes allegations that Trump campaign officials coordinated with Russia to tilt the election in the Republican's favour - is gathering pace.

The establishment of a grand jury will allow Mueller - a former FBI director - to subpoena documents and get sworn testimony. It could well lead to criminal indictments.

"It's a significant escalation of the process," national security attorney Bradley Moss told AFP.

"You don't empanel a grand jury unless your investigation has discovered enough evidence that you feel reflects a violation of at least one, if not more, criminal provisions," he said.

"If you secure an indictment, your next step is to arrest the defendant."

Presidential lawyer Ty Cobb said he was not aware that a grand jury had been convened.

"Grand jury matters are typically secret," Cobb said, adding that "the White House favours anything that accelerates the conclusion of his work fairly."

"The White House is committed to fully cooperating with Mr Mueller."

White House spokeswoman Sarah Huckabee Sanders said the president was not likely the subject of the investigation.

"Former FBI director Jim Comey said three times the president is not under investigation and we have no reason to believe that has changed," she said.

Justice Department spokeswoman Sarah Isgur Flores declined to comment on the report.

Trump has repeatedly denied allegations of collusion, saying he is the victim of a political "witch hunt" and "fake news."

But he has been forced to acknowledge that his eldest son, Donald Jr, his son-in-law Jared Kushner and his then campaign advisor Paul Manafort did meet a Kremlin-connected lawyer to get dirt on Hillary Clinton.

Mueller is also said to be investigating Trump's financial records unrelated to Russia or the election, CNN reported.

Trump has publicly warned Mueller that his financial dealings should be out of bounds and investigating them would cross a red line.

If called to testify before a grand jury, Trump would not be the first president to do so. Then president Bill Clinton was forced to give details about his relationship with Monica Lewinsky, evidence that was used in his impeachment.

Thursday's revelations will only fuel speculation that Trump may try to curb the investigation by firing Mueller.

Two US senators introduced a bipartisan bill Thursday to pre-empt that move by insulating Mueller.

The legislation, sponsored by Democrat Chris Coons and Republican Thom Tillis, would bar a president from directly firing the special counsel without a judicial review.

Under the bill, Mueller would be allowed to challenge his removal in court in the event he is fired without good cause.

"A back-end judicial review process to prevent unmerited removals of special counsels not only helps to ensure their investigatory independence, but also reaffirms our nation's system of check and balances," Tillis said in a statement.

Coons added: "Ensuring that the special counsel cannot be removed improperly is critical to the integrity of his investigation."