US President Donald Trump has fired Secretary of State Rex Tillerson, naming CIA Director Mike Pompeo as his replacement.
Thanking Mr Tillerson for his service, Mr Trump tweeted that his new top diplomat would do "a fantastic job".
Mr Pompeo is a former hardline conservative Republican lawmaker from Kansas and a Trump loyalist. In 2014, he defended the CIA officers who waterboarded detainees as "patriots".
Mr Tillerson, a former chief executive of ExxonMobil, was only appointed to the job just over a year ago.
The Department of State said Mr Tillerson had not spoken to the president and was "unaware of the reason" for his firing.
Under Secretary Steve Goldstein said: "The Secretary had every intention of staying because of the critical progress made in national security."
According to the Associated Press, White House chief of staff John Kelly called Mr Tillerson on Friday and advised him to watch out for a presidential tweet about him.
Mr Kelly did not tell Mr Tillerson when the tweet would be posted or what it might say, the news agency reported.
Mr Tillerson was on an official tour of Africa last week when he was caught unawares by Mr Trump's agreement to meet North Korean leader Kim Jong-un.
His team said he was feeling unwell on Saturday and later in the weekend the state department said he would cut short his tour by a day.
"I felt like, look, I just need to get back," Mr Tillerson told the Washington Post.
Gina Haspel appointed CIA director
The president also nominated Gina Haspel to become the first female director of the CIA.
A US Senate report found that Ms Haspel ran a notorious CIA prison in Thailand, where prisoners were waterboarded in 2002.
The CIA deputy director was also accused of destroying dozens of videotapes of interrogations at the camp.
Both the new secretary of state and CIA director will have to be confirmed by the Senate.
Rift between Trump and Tillerson
Reports had swirled since last year of a schism in the Trump administration between the commander-in-chief and his top diplomat.
On Monday, Mr Tillerson blamed Russia for the poisonings in England of a former Russian double agent and his daughter. Earlier at the White House, press secretary Sarah Sanders had refrained from saying Moscow was responsible.
A senior White House official said Mr Trump asked Mr Tillerson to step down on Friday but did not want to make it public during the Secretary of State's trip to Africa.
The official said Trump wanted Pompeo in place before the U.S. president's planned talks with North Korean leader Kim Jong Un and trade negotiations.
Mr Tillerson was forced to convene a news conference last October to deny claims he planned to quit, though he did not address a report that he had referred to his boss as a moron after a Pentagon meeting.
Last autumn, Mr Trump publicly undercut the former Texas oilman by tweeting that he was "wasting his time" trying to negotiate with North Korea.
In December, the secretary of state departed from administration talking points when he offered to begin direct talks with Pyongyang without preconditions.
The White House - which insisted North Korea must first accept any negotiations would be about giving up its nuclear arsenal - distanced itself from his remarks.
Mr Tillerson was reported to be astonished at how little Mr Trump grasped the basics of foreign policy.
The Republican president, meanwhile, was irritated by Mr Tillerson's body language during meetings, the New York Times reported.
The secretary of state was said to roll his eyes or slouch when he disagreed with Mr Trump's decisions.
The 65-year-old arrived back in Washington before dawn on Tuesday to learn he was out of a job a few hours later.
Speaking to reporters outside the White House on Tuesday, Mr Trump said his differences with Mr Tillerson came down to personal "chemistry".
"We got along actually quite well, but we disagreed on things," said the president.
"When you look at the Iran deal, I think it's terrible. I guess he thought it was OK.
"I wanted to either break it or do something and he felt a little bit differently, so we were not really thinking the same.
"With Mike, Mike Pompeo, we have a very similar thought process. I think it's going to go very well.
"Rex is a very good man, I like Rex a lot."
Mr Tillerson is the latest in a long list of senior officials who have either resigned or been fired since Mr Trump took office.
- BBC / Reuters