FBI director James Comey has said there was no basis for Donald Trump’s claims to have been wiretapped by Barack Obama, but confirmed for the first time that the agency is investigating possible collusion between the United States President's campaign and the Russian government to influence the outcome of the presidential election.

Comey had previously refused to comment on the existence of any such investigation, but during his opening statement at the first public hearing held in Congress on the matter, he said he had received authorization from the Department of Justice to confirm that such an investigation was under way. 

Comey told lawmakers that his agency is looking into the links between Donald Trump's campaign team and the Russian government, and whether there was any "coordination" of the Kremlin's activity vis-a-vis the US election and the magnate's campaign.

The counter-intelligence investigation into Trump-Moscow links began in late July 2016 and is still ongoing.

The FBI chief added that the investigation will also examine if any type of crime was committed regarding the leaking of e-mails stolen from the Democratic National Committee and Hillary Clinton's then-campaign manager, John Podesta. 

Comey’s appearance, flanked by the NSA director, Adm Michael Rogers, marked a remarkable and unprecedented threshold in US political history, putting beyond doubt that a sitting’s president’s entourage was under investigation for possibly conniving with a foreign adversary to put that president in power, as reported in The Guardian.

Given the delicate nature of the investigation and the fact that it is currently in progress, for security reasons Comey was not able to publicly respond to many of the questions posed to him by lawmakers and he also warned that the leaking of certain documents could carry a 10-year prison sentence.

The top-ranking Democrat on the committee, Rep. Adam Schiff, said that if Trump's campaign or anyone associated with it helped or encouraged the Russians, that would not only be a serious crime but would constitute one of the most important betrayals in US history.

On the other side, the New York Times reported that a Ukrainian lawmaker released an invoice that appeared to show a payment of $750,000, disguised as a sale of computers, from a pro-Russian party in Ukraine to Paul Manafort, Mr. Trump’s onetime presidential campaign manager.

In other testimony, Comey told lawmakers that "We have no information to support" President Trump's Twitter claim that former President Barack Obama wiretapped Trump Tower before the election.

"We have no information to support those tweets," he added several times in response to various questions by lawmakers.

The NSA director, Mike Rogers, said in response to questions that he had no knowledge of anyone asking the British or any other ally to wiretap the GOP presidential nominee, thus refuting another claim made by Trump.

 "I've seen nothing on the NSA side that we engaged in such activity nor that anyone engaged in such activity," Rogers said, going on to specifically deny having any evidence that British intelligence wiretapped Trump at the Obama's behest.

During the hearing, Trump’s tweeted a commentary that signaled he was misrepresenting what was happening: 

"The NSA and FBI tell Congress that Russia did not influence electoral process," he tweeted, from his official @POTUS account.

The tweet made its way to the committee, with the result that Comey and Rogers were confronted with it. Again they said there was no basis for the assertion, reported The Guardian.

“We’ve offered no opinion, have no view ... on potential impact, because it’s not something that we’ve looked at,” Comey said. “It certainly wasn’t our intention to say that today because we don’t have any information on that subject. And it wasn’t something that was looked at.”

Just hours after FBI director James Comey confirmed that there was a federal investigation into possible collusion between the Trump campaign and Russia during the 2016 presidential race, Donald Trump spoke to a crowd of 18,000 supporters at a Kentucky rally of NFL quarterbacks and healthcare reform but failed to mention FBI's Russia investigation.