Donald Trump has insisted he has "the complete power to pardon", fuelling speculation he is considering using the device to extricate himself and members of his team from an investigation into collusion with Russia to interfere in the US election.

The President made the statement during an early-morning stream of posts on Twitter, saying: "While all agree the U. S. President has the complete power to pardon, why think of that when only crime so far is LEAKS against us. FAKE NEWS."

Although the President's tweet hinted there was no need to use the power at the moment, because nothing wrong had been done, his rhetoric has raised concerns among senior opposition politicians and academics.

Scholars have raised questions about the scope of the President's legal authority in issuing pardons. If Trump moved to pardon himself sometime in the future, the US Supreme Court might have to decide on the constitutionality, some have speculated.

Senator Mark Warner, a Democrat who sits on the House Intelligence Committee, said: "The possibility that the President is considering pardons at this early stage in these ongoing investigations is extremely disturbing. Pardoning any individuals who may have been involved would be crossing a fundamental line."

A Democratic Party spokesperson told the BBC that the claims were "extremely disturbing".

Mr Trump has also claimed that leaks regarding Attorney General Jeff Sessions are illegal. A recent report in the Washington Post quotes Justice Department insiders, who say that Mr Sessions met with the former Russian Ambassador to the US Sergey Kislyak during the 2016 campaign and discussed key policy positions toward Russia. Mr Sessions claimed that he had not met with Russians during the campaign; he also later recused himself from oversight of the investigation into Russia's 2016 election influence.

It comes amid mounting pressure on the President and his administration over their alleged links with the Kremlin's purported attempts to influence the vote last November in his favour.

Just yesterday, White House deputy press secretary Sarah Huckabee Sanders refused to rule out the possibility Mr Trump would use his pardon power to shield himself, his family, and his administration from federal lawsuits.

Beschloss: 'If Donald Trump thinks he can pardon himself we are on our way to constitutional crisis'

Ms Huckabee Sanders addressed reporters during her first press briefing following the resignation of Sean Spicer, who had announced his resignation as White House press secretary earlier that day. She is reported to be the favourite to take his place as press secretary.

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"I'd refer you to the comments that have already been made by the outside counsel," Ms Huckabee Sanders said when asked about the President's position on pardons.

Hours earlier, the emergence of Russian court documents seen by Reuters showed that the Russian lawyer who met Donald Trump Jr before his father's election counted the country's FSB security service among her clients for years.

There is no suggestion that Natalia Veselnitskaya was an employee of the Russian government or intelligence services, and she has denied having anything to do with the Kremlin.

But the fact she represented the FSB in a court case prompted intensified questions of the Trump administration.

Following the tweet about his power to pardon, the President embarked on a familiar tirade about Hillary Clinton emails and the sacked FBI director James Comey.

He went on to suggest Ms Clinton, the Democratic candidate he defeated to enter the White House, had "deleted (& acid washed) her 33,000 emails".

Mr Trump compared this with the fact his son, Donald Jr "openly gave his e-mails to the media & authorities".

Following Mr Trump Jr's release of the emails, it emerged he had done so minutes before the New York Times was due to publish details of their contents.