A new and damaging leak on the bizarre pronouncements of President Donald Trump reveals that he has described former FBI director James Comey as a 'real nut job'.

The revelation in the New York Times comes after Comey, a committed Christian who is a member of the United Methodist Church who majored in chemistry and religion when he was a student at at the College of William and Mary in Williamsburg, was fired by Trump.

The New York Times reported that Trump told Russian officials in the Oval Office that firing the Comey had relieved 'great pressure'.

He said: 'I just fired the head of the FBI. He was crazy, a real nut job,' the Times reported. 'I faced great pressure because of Russia. That's taken off.' He also said he is not personally under investigation.

The conversation reinforces the notion that the president dismissed Comey primarily because of the bureau's investigation into possible collusion between Russia and the Trump election campaign, according to the Times.

Spokesman Sean Spicer said in a statement: 'The President has always emphasised the importance of making deals with Russia as it relates to Syria, Ukraine, defeating ISIS and other key issues for the benefit and safety of the American people.

'By grandstanding and politicising the investigation into Russia's actions, James Comey created unnecessary pressure on our ability to engage and negotiate with Russia. The investigation would have always continued, and obviously, the termination of Comey would not have ended it. Once again, the real story is that our national security has been undermined by the leaking of private and highly classified conversations.'

The conversation took place when Trump met Russian Foreign Minister Sergei Lavrov and Russia's ambassador to Washington in the Oval Office the day after the firing. 

Trump has also been hit by embarrassing leaks that a senior adviser was a 'person of interest' in the Russia collusion investigation.

The Washington Post, citing sources familiar with the matter, did not identify the senior Trump adviser except to say that the person of interest was close to Trump, a Republican who entered the White House four months ago.

Additional reporting by Reuters