Trump ordered Mueller's firing but backed off: Report

US President Donald Trump last year ordered the firing of special counsel Robert Mueller, who is conducting an investigation into alleged Russian meddling in the 2016 presidential election, but backed off after the White House counsel threatened to resign, a media report claimed.

The news report comes a day after Trump said he was willing to be questioned under oath by Mueller.

Trump's opponents allege that the Russian interference helped him win the polls. But he denies any collusion between the Trump campaign and the Russians.

Mueller, the former FBI director, has interviewed several members of the Trump campaign, Trump's family members, colleagues in the Cabinet and present and former White House officials.

He has been seeking the interview with Trump as part of his investigation.

According to media reports, Mueller wants to interview Trump on his decision to fire national security advisor Michael Flynn and FBI director James Comey.

"President Trump ordered the firing last June of Robert S Mueller III, the special counsel overseeing the Russia investigation, according to four people told of the matter, but ultimately backed down after White House counsel (Don McGahn) threatened to resign rather than carry out the directive," The New York Times reported.

Trump's personal attorney Ty Cobb refused to comment.

"We decline to comment out of respect for the Office of the Special Counsel and its process," he said.

Indian-American Congresswoman Pramila Jayapal slammed trump for his reported decision.

"Firing Robert Mueller is a red line, full stop," she said.

"The Special Counsel is widely respected on both sides of the aisle and his investigation into grave breaches of our electoral system is absolutely critical to our democracy – any attempt to threaten his investigation is an affront to accountability and potential legal consequences for collusion with a foreign power," Jayapal said in a late-night statement.

Jayapal said this is truly a make-or-break moment for the country's system of checks and balances.

"Today's New York Times report lays out what can only be described as despotic and authoritarian behaviour by Donald Trump – with strong overtones of Nixon's Watergate.

"Now is the time for Republicans to stand up and be counted – and for all Americans to oppose the naked abuse of power by a dangerous and unhinged man who is utterly unfit to be president," Jayapal said.

Senator Mark Warner, Vice Chairman of the Senate Select Committee on Intelligence warned Trump against firing Mueller.

"I've said it before, and I am saying it again: firing the Special Counsel is a red line that the President cannot cross.

"Any attempt to remove the Special Counsel, pardon key witnesses, or otherwise interfere in the investigation, would be a gross abuse of power, and all members of Congress, from both parties, have a responsibility to our Constitution and to our country to make that clear immediately," he said.

According to The Times, Mueller learned about the episode in recent months as his investigators interviewed current and former senior White House officials in his inquiry into whether the president obstructed justice.

Investigators are assessing if the Trump campaign colluded with Russia to influence the election in his favour a claim denied by Trump and Russia.

Investigators will also determine if Trump obstructed the inquiry.

The US intelligence community has already concluded that Moscow tried to sway the presidential election in favour of Trump.