Another week, another stunning high-profile sacking at the White House.

Donald Trump has announced — in a tweet — that his national security adviser, H.R. McMaster, will be replaced in the key role.

The US president said he has chosen John Bolton to be his new national security adviser. Bolton is a foreign policy "hawk" who has advocated using military force against Iran and North Korea and taken a hard line against Russia.

Former national security adviser H.R. McMaster has left the building. Photo / AP
Former national security adviser H.R. McMaster has left the building. Photo / AP

Bolton, 69, who has long been a polarising figure in Washington foreign policy circles, becomes Trump's third national security adviser in 14 months.

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Trump said Gen McMaster has done "an outstanding job & will always remain my friend". Bolton will take over on April 9.

Talk of the departure had been brewing for some days, despite the White House insisting Gen McMaster and the President had a good working relationship just one week ago.

Trump has repeatedly clashed with Gen McMaster, a respected three-star general, and talk that Gen McMaster would soon leave the administration had picked up in recent weeks.

His departure follows Trump's dramatic ouster of Secretary of State Rex Tillerson last week.

It also comes after someone at the White House leaked that Trump was urged in briefing documents not to congratulate Russian President Vladimir Putin about his recent re-election win.

The President did it anyway.

Gen McMaster was brought in after Trump's first national security adviser, Michael Flynn, was dismissed.

Flynn resigned after disclosures that he had discussed US sanctions on Russia with Moscow's Ambassador to the United States before Trump took office, and then lied about it both publicly and in an interview with the FBI.

He also admitted he misled Vice President Mike Pence about the conversations.

In a statement released by the White House, Gen McMaster said he would be requesting retirement from the US Army effective this summer, adding that afterwards he "will leave public service".

The White House said McMaster's exit had been under discussion for some time and stressed it was not due to any one incident.

CHANGE THROUGH WAR

Writing in Slate, Fred Kaplan the author of Dark Territory: The Secret History of Cyber War, said Bolton's appointment "puts us on the path to war".

Kaplan, writing an article under the alarming headline "It's time to panic," says Bolton has repeatedly called for a first strike on North Korea and for ditching a nuclear arms deal with Iran "and the bombing of that country too."

He warns Bolton's agenda isn't "peace through strength" - the traditional stance of Republican presidents since Ronald Reagan - but rather regime change through war.

"He is a neo-con without the moral fervour of some who wear that label — i.e., he is keen to topple oppressive regimes not in order to spread democracy but rather to expand American power," Kaplan writes.

Professor of Political Science at Pusan National University and leading Korean expert Robert E Kelly warned the appointment was bad news.

Prof Kelly said this appointment was a good enough reason to cancel the planned Trump-Kim summit.

CNN White House correspondent Kaitlan Collins tweeted that the President and Bolton had been discussing for weeks how Gen McMaster could be replaced.

She said a source told her Bolton had promised Trump "he wouldn't start any wars" if he selected him as the new national security adviser.

She also said the POTUS and his Gen McMaster never got on and the only reason he survived for as long as he has is because advisers were skeptikal of how it looked to have three people in the role in a year.

According to Collins, Bolton wasn't expecting the President's announcement when it happened.

Gen McMaster's exit is the latest in a string of high-profile departures from the White House that began with Flynn and has also included chief of staff Reince Priebus, chief strategist Steve Bannon, economic advisor Gary Cohn and Tillerson.

A vocal advocate of the Iraq war, Bolton's appointment had been fiercely opposed by many within Trump's inner circle, most notably the coterie of military officers who have experienced the brutality of war first hand.