Donald Trump has sacked Rex Tillerson as his secretary of state and will replace him with CIA director Mike Pompeo.
The US president asked Mr Tillerson to step aside after months of speculation that the pair had fallen out.
The move amounts to a major shakeup in Mr Trump’s national security team and comes despite denials in the past from the president that he wanted Mr Tillerson gone.
It triggered a war of words within the US government as the State Department accused the president of not talking to Mr Tillerson before the sacking.
Mr Trump cited the pair’s differences on the Iran nuclear deal, which the president wants to scrap, when asked about the reason for the change.
The announcement comes just hours after Mr Tillerson went substantially further than the White House in linking the UK spy poisoning to Russia.
CNN reported that Mr Tillerson first found out about the sacking from Mr Trump’s tweet. He had just returned from diplomatic trip to Africa.
Tensions between Mr Trump and Mr Tillerson came to a head when the latter refused to deny reports he called the president a “moron” last year.
The pair have also publicly spared over the approach to North Korea, with Mr Trump reprimanding Mr Tillerson in tweets for believing talks with the regime could end their nuclear programme.
Mr Tillerson, a former oil executive, will be replaced by Mr Pompeo, who as the head of the CIA is involved in the president’s daily intelligence briefly – providing his appointment is confirmed by Congress.
There have been reports that Mr Trump has asked Mr Pompeo for advice about topics beyond intelligence before Christmas, when it was said the president was considering making the switch.
Mr Trump said in a statement to the Washington Post: “I am proud to nominate the Director of the Central Intelligence Agency, Mike Pompeo, to be our new Secretary of State.
“Mike graduated first in his class at West Point, served with distinction in the U.S. Army, and graduated with Honors from Harvard Law School.
“He went on to serve in the U.S. House of Representatives with a proven record of working across the aisle.”
He added: “I want to thank Rex Tillerson for his service. A great deal has been accomplished over the last fourteen months, and I wish him and his family well.”