President Donald Trump has fired Michael Atkinson, the inspector general for the intelligence community who handled the whistleblower complaint that triggered Trump's impeachment .

Trump informed the Senate intelligence committee on Friday of his decision to fire Atkinson, according to a letter obtained by The Associated Press.

Trump said in the letter that it is "vital" that he has confidence in the appointees serving as inspectors general, and "that is no longer the case with regard to this inspector general."

Donald Trump was impeached by the House after illegally pressuring the Ukraine President to investigate his political rival Joe Biden. (AP)

He did not elaborate, except to say that "it is extremely important that we promote the economy, efficiency and effectiveness of federal programs and activities," and that inspectors general are critical to those goals.

Atkinson was the first to inform Congress about an anonymous whistleblower complaint last year that described Trump's pressure on Ukraine to investigate Democrat Joe Biden and his son. That complaint prompted a House investigation that ultimately resulted in Trump's impeachment.

In letters to lawmakers in August and September, Atkinson said he believed the complaint was "urgent" and "credible." But the acting Director of National Intelligence at the time, Joseph Maguire, said he did not believe it met the definition of "urgent," and tried to withhold the complaint from Congress.

Inspector-General Michael Atkinson was fired by Donald Trump for handling a whistleblower complaint about the president's illegal activities. (AP)

After a firestorm, the White House released the complaint, revealing that Trump had asked Ukrainian President Volodymyr Zelenskiy in a July call to investigate the Bidens. The House launched an inquiry, and three months later voted to impeach Trump. The Republican-led Senate acquitted Trump in February.

Trump said in the letter that he would nominate an individual "who has my full confidence" at a later date.

Democrats reacted swiftly to Atkinson's removal. The top Democrat on the Senate intelligence panel, Virginia Sen. Mark Warner, said it was "unconscionable" that Trump would fire Atkinson in the midst of the coronavirus pandemic.

The top senators on the Intelligence Committee, Democrat Mark Warner and Republican Richard Burr. (AAP)

"We should all be deeply disturbed by ongoing attempts to politicise the nation's intelligence agencies," Warner said.

House Intelligence Committee Chairman Adam Schiff, D-Calif., who led the House impeachment inquiry, said "the president's dead of night decision puts our country and national security at even greater risk."

Senate Democratic Leader Chuck Schumer, D-N.Y., said in a statement that "President Trump fires people for telling the truth."

Senate Minority Leader Chuck Schumer walks away from a throng of reporters in the Capitol. (AP)

Atkinson's firing is part of a larger shakeup in the intelligence community. Maguire, the former acting Director of National Intelligence, was also removed and replaced by a Trump loyalist, Richard Grenell. Trump has nominated Texas Rep. John Ratcliffe to the permanent position, but the Senate has yet to move on his nomination.

Tom Monheim, a career intelligence professional, will become the acting inspector general for the intelligence community, according to an intelligence official who was not authorised to discuss personnel changes and spoke only on condition of anonymity.