WASHINGTON – President Trump said Tuesday he has ousted Secretary of State Rex Tillerson and plans to nominate CIA Director Mike Pompeo to replace him as the nation’s top diplomat, orchestrating a major change to his national security team amid delicate outreach such as possible talks with North Korea.

As Tillerson traveled through Africa, White House chief of staff John Kelly called to wake him up in the wee hours there Saturday to alert him that he would soon be replaced and to return to Washington as soon as possible, White House officials said.

Tillerson cut his trip short Monday to fly home, and his spokesman said Tuesday that the secretary of state was “unaware of the reason” for his firing and had not spoken directly with Trump.

Officials at the State Department and throughout the national security community were flummoxed by the news.

Tension between Trump and Tillerson has simmered for many months, but the president and his top diplomat reached a breaking point over the past week, and media inquiries about the fraught relationship accelerated the timing of the ouster, White House officials said.

Trump told reporters Tuesday that he had been considering removing Tillerson for “a long time” because they disagreed over U.S. strategy in key areas of foreign policy, such as the Iran nuclear deal, the approach to North Korea and the tone of U.S. diplomacy.

“I actually got along well with Rex but really it was a different mind-set, a different thinking,” Trump said as he departed the White House for a trip to California. “When you look at the Iran deal, I think it’s terrible. I guess he thought it was OK . . . 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.”

Trump selected Gina Haspel – the deputy director at the CIA – to succeed Pompeo at the CIA. She would become the first woman to run the spy agency. Both Haspel and Pompeo would need to be confirmed by the Senate at a time when the closely divided chamber has stalled on confirming dozens of Trump nominees.

Haspel, in particular, could come under added scrutiny over her past role running one of the CIA “black site” prisons where detainees were subjected to waterboarding and other interrogation methods widely denounced as torture.

The announcement of Tillerson’s departure sent shock waves across the globe. Many U.S. diplomats and foreign leaders reacted with disbelief because they assumed Tillerson had finally begun to settle into his job after rumors of his ouster had swirled for months – even taking on a nickname, Rexit.

In a statement first issued to The Washington Post, Trump praised both Pompeo and Haspel.

“I am proud to nominate the Director of the Central Intelligence Agency, Mike Pompeo, to be our new Secretary of State,” Trump said. “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.”

The president continued: “Gina Haspel, the Deputy Director of the CIA, will be nominated to replace Director Pompeo and she will be the CIA’s first-ever female director, a historic milestone. Mike and Gina have worked together for more than a year, and have developed a great mutual respect.”

Trump also had words of praise for Tillerson despite their well-documented rifts: “Finally, 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.”

A spokesman for Tillerson said the secretary of state has not spoken directly with Trump about the move.

“The secretary had every intention of staying because of the critical progress made in national security and other areas,” Steve Goldstein, undersecretary of public diplomacy for the State Department, said in a statement.

“He will miss his colleagues greatly at the Department of State, and the foreign ministers he’s worked with throughout the world,” Goldstein continued. “The secretary did not speak to the president, and is unaware of the reason. He is grateful for the opportunity to serve, and believes strongly that public service is a noble calling.”

The president has long clashed with Tillerson, who he believes is “too establishment” in his thinking. Trump felt it was important to make the change now, as he prepares for possible high-stakes talks with North Korean leader Kim Jong Un, as well as upcoming trade negotiations, three White House officials said.

“I am deeply grateful to President Trump for permitting me to serve as Director of the Central Intelligence Agency and for this opportunity to serve as Secretary of State,” Pompeo said in a statement. “His leadership has made America safer and I look forward to representing him and the American people to the rest of the world to further America’s prosperity. Serving alongside the great men and women of the CIA, the most dedicated and talented public servants I have encountered, has been one of the great honors of my life.”

Haspel said in a statement that she was excited about her promotion.

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“After 30 years as an officer of the Central Intelligence Agency, it has been my honor to serve as its Deputy Director alongside Mike Pompeo for the past year,” she said. “I am grateful to President Trump for the opportunity, and humbled by his confidence in me, to be nominated to be the next Director of the Central Intelligence Agency.”

On the flight back from Nigeria, Tillerson appeared to break with the White House in his assessment of the poisoning of a former Russian spy and his daughter in Britain. He singled out Russia as responsible for the attack, echoing the finger-pointing of the British government.

“It came from Russia,” Tillerson said, according to the Associated Press. “I cannot understand why anyone would take such an action. But this is a substance that is known to us and does not exist widely.”

Earlier Monday, White House press secretary Sarah Huckabee Sanders condemned the attack as “reckless, indiscriminate and irresponsible,” and expressed solidarity with Britain, but would not say whether the United States believes Russia was behind it.

Tillerson was especially frustrated when Trump last Thursday unilaterally agreed to the meeting with the North Korean leader Kim while Tillerson was traveling in Africa, according to officials familiar with his thinking.

Tillerson had long expressed interest in a diplomatic solution to the nuclear standoff with North Korea, and was upset to have been left totally out of the loop when Trump decided to move forward, according to a White House official.

Foggy Bottom was also acutely aware – and chagrined – that Pompeo did not cite Tillerson when he appeared on television shows Sunday to explain the North Korea developments.

Pompeo long has been mentioned as Tillerson’s most likely replacement. As CIA director, the former Republican lawmaker from Kansas developed a warm relationship with Trump, often delivering the President’s Daily Brief to Trump in person and racing over to the West Wing at a moment’s notice to field the president’s queries on a range of topics.

Pompeo often is found in a host of meetings that do not necessarily deeply involve his agency, simply because Trump likes him, said one White House official.

Sen. Tom Cotton, R-Ark. was initially mentioned as a replacement for Pompeo, but Trump opted to promote from within by elevating Haspel.

Speculation about his ouster has come in waves, including in October after NBC News reported that Tillerson had called Trump a “moron.”

Tillerson, 65, spent his career at ExxonMobil, climbing the ranks at the oil giant to become chief executive officer, where he cut deals across the Middle East and in Mexico. Having never worked in government before being named secretary of state, he struggled to adapt to Washington’s ways and the administration’s culture of backstabbing.

Tillerson emerged as one of the strongest voices in the administration critical of Russia. For months, he has been saying Russia clearly meddled in the 2016 U.S. election, even as Trump shied away from any critical remarks.

Trump seemed to resent pressure to stay the course on such issues as China’s trade practices, the war in Afghanistan and the Iran nuclear deal, those people said.

Tillerson pushed Trump to preserve the Iran accord, at least for now, with a July pronouncement that Iran was meeting its end of the bargain – which curbs Iran’s nuclear program in exchange for lifting international sanctions.

Trump said in a Wall Street Journal interview that he regretted making that determination. In October, Trump kept in place the sanctions waivers, but warned he may not continue the policy when the next review is due next month.

Although Tillerson supported the approach to the war in Afghanistan that Trump announced last year, he felt no need to frame U.S. goals in the same maximal terms as the commander in chief. Where Trump proclaimed on Aug. 21 that “our troops will fight to win,” Tillerson laid out a much more modest agenda.

The Washington Post’s Josh Dawsey, John Hudson, Carol D. Leonnig, Carol Morello and Brian Murphy contributed to this report.

Former U.S. Secretary of State Rex Tillerson