WASHINGTON, D.C. — After 14 months of private tensions and public disputes, President Donald Trump on Tuesday ousted his secretary of state, replacing Rex Tillerson with CIA Director Mike Pompeo in a major shake-up of his national security and foreign policy team.

Trump announced the change in a Twitter message a day after Tillerson abruptly cut short a weeklong trip to Africa and returned to Washington.

State Department officials said Tillerson had not spoken to Trump about his dismissal and only learned it was official via Twitter. Tillerson also was not given advance warning last week when Trump abruptly decided to accept an invitation for a summit with North Korean leader Kim Jong Un.

Speaking to reporters before he boarded Air Force One for his first visit to California as president, Trump said he and Tillerson “disagreed on things.”

“We’ve been talking about this for a long time,” Trump said, citing the Iran nuclear deal as one of their points of disagreement. Tillerson has urged Trump to stay in the landmark nuclear disarmament deal, but the president has vowed to withdraw by mid-May if it is not renegotiated.

“So we were not thinking the same,” Trump said. “With Mike Pompeo, we have a similar thought process.”

The president said he wished Tillerson well. “I’ll be speaking to Rex over a long period of time,” he added. “I actually got on well with Rex but it was a different mindset.”

In the tweet, Trump briefly thanked Tillerson for his service as the nation’s top diplomat and praised Pompeo, saying he would do a “fantastic job” as the country’s top diplomat.

Gina Haspel, the CIA’s deputy director, will replace Pompeo as head of the nation’s chief spy service. If confirmed, she will be the first woman to lead the agency as it faces new threats from Russia, China and other rivals and adversaries.

Tillerson clashed repeatedly with Trump during his 14 months at State, and famously declined to deny published reports last summer that he had called Trump a moron.

In addition to resisting Trump’s effort to scrap the 2015 deal with Iran to curb its nuclear ambitions, he opposed Trump’s plan to move the U.S. Embassy in Israel to Jerusalem.

And despite a record of high-stakes business dealings with Russia in his former job as chief executive of Exxon Mobil Corp., Tillerson has voiced more public mistrust of Moscow than Trump has.

On Monday, Tillerson again departed from the White House position — denouncing Russia for a poison attack in Britain that targeted a former Russian spy, who has criticized President Vladimir Putin, and his daughter. More than 20 people, including first responders, were injured by the chemical agent.

The attack “clearly came from Russia” and will “trigger a response,” Tillerson told reporters aboard his plane as he returned from Africa. Earlier in the day, the White House had conspicuously declined to join British officials in blaming Russia for the attack.

But even as he differed with Trump, Tillerson had few allies on Capitol Hill or among the diplomats and civil servants in the sprawling department he headed. Many in the foreign service saw him as aloof and distant as he pursued a plan to trim and reorganize the department’s bureaucracy.

By contrast, Pompeo, a former congressman, has skills Tillerson lacks, said Michael Allen, who worked in the George W. Bush White House and advised the Trump transition.

“He can do media, he does the Hill, he does everything Tillerson didn’t do,” Allen said. “Most of all, he has Trump’s confidence.”

Pompeo often briefs Trump in person in the Oval Office on critical intelligence issues, and over the last several weeks has played a pivotal role in brokering messages from South Korean officials about North Korean leader Kim Jong Un’s willingness to meet Trump.On North Korea, Tillerson has largely been left on the sidelines. He memorably said that the U.S. and North Korea were still a long way from negotiations, just hours before plans for a summit between Trump and Kim were announced.

Tillerson, long a moderating voice in a chaotic administration, returned at 4 a.m. Tuesday from Africa, where he was traveling and as he struggled to defend his role after having been excluded from Trump’s decision to meet with North Korean leader Kim Jong Un.