Trump fires back at critics over FBI chief sacking

US President Donald Trump defied fierce criticism on Wednesday over the abrupt firing of FBI Director James Comey, inviting Russia's foreign minister to the White House even as Democrats demanded an independent probe of Moscow's alleged meddling in the US elections.

Trump's decision to terminate Comey on Tuesday immediately drew comparisons to the Watergate scandal that brought down Richard Nixon and stunned Washington.

"James Comey will be replaced by someone who will do a far better job, bringing back the spirit and prestige of the FBI," Trump tweeted.

Under Comey, who was appointed four years ago, the FBI was investigating whether Trump campaign aides colluded with Russia in an attempt to sway the US election in the Republican's favour.

Trump wrote a letter to Comey, trying to distance himself from the ever-deepening scandal over Russia's involvement in the election.

"I greatly appreciate you informing me, on three separate occasions, that I am not under investigation," Trump wrote.

Trump said he was acting on recommendations of his attorney general, Jeff Sessions, and deputy attorney general, Rod Rosenstein, who accused Comey of "serious mistakes" in his handling of an investigation into Hillary Clinton's email.

TRT World's Arabella Munro has this report.

The FBI director had antagonised all sides, first angering Republicans by closing the email probe against the Democratic candidate Clinton and then Democrats by reopening it days before the November presidential election.

However, Democrats and some Republicans see the move to get rid of Comey as an assault on the FBI's Russia probe and demanded that it be turned over to an independent special prosecutor or commission.

"This is nothing less than Nixonian," said Senator Patrick Leahy of Vermont, who called Trump's official justification for firing Comey "absurd."

Senate Democratic leader Chuck Schumer said Trump had made a "big mistake."

Unless the administration appoints an independent special prosecutor to probe the Russian meddling, Schumer added, "every American will rightly suspect that the decision to fire Director Comey was part of a coverup."

Trump fired back on Twitter.

Republicans, many of whom have fallen into line behind Trump after initial reluctance, also sought to distance themselves from the president. "I am troubled by the timing and reasoning of Director Comey's termination," said Senator Richard Burr.

During testimony to Congress last month, Comey overtly challenged the president, flatly rejecting his explosive claim that he was wiretapped by his predecessor. And despite Trump's dismissal of suggestions his team colluded with Moscow as "fake news," it had become increasingly clear that Comey had set his sights on the issue of Russia's election meddling, which has stalked Trump's presidency from the start.

The White House said the search for a new FBI director is now underway.