President Donald Trump has dismissed U.S. Secretary of State Rex Tillerson.Trump announced the change in a message on the social media network Twitter early Tuesday.The announcement came four hours after Tillerson returned to Washington from a trip to Africa.Trump said he would nominate Mike Pompeo,the director of the Central Intelligence Agency, to replace Tillerson.The move comes as the administration prepares for important talks with North Korea."Mike Pompeo, Director of the CIA, will become our new Secretary of State," Trump tweeted."He will do a fantastic job! Thank you to Rex Tillerson for his service!Gina Haspel will become the new Director of the CIA,and the first woman so chosen. Congratulations to all!"Both appointments must be confirmed by the Senate.Speaking this morning, the president said he and Tillerson "disagreed on things,"including their opinions about the Iran nuclear deal.For months, officials have spoken about Trump's dissatisfaction with Tillersonalthough Tillerson insisted he did not plan to leave.Rumors about disagreements between Trump and Tillerson began spreading last year.In October, NBC News reported that Tillerson called the president a "moron,"something Tillerson never actually denied.Tillerson continued to insist his relationship with the president was solidand denied rumors of problems between them.Two officials familiar with the situation saidthat Tillerson had been fired by Trump on Friday, while in Africa.However, that was not clear as Tillerson returned to Washington early Tuesday from Nigeria.But Tillerson had cut short his trip by one night.He told reporters he had been sick in Africa and had not slept wellbecause of urgent issues, including the North Korea announcement."I felt like, look, I just need to get back," Tillerson said.One top Trump administration official said dismissing Tillersonhad been discussed at many levels for a long time.The official said the situation with North Koreaand the invitation to meet brought more urgency to the decision.Two officials said Trump wanted to have a new team in placebefore the meeting with North Korean leader Kim Jong Un and also before trade talks.The officials were not authorized to speak publicly and demanded that their names not be released.Tillerson also was known for his ties with Russia and Russian President Vladimir Putin.He developed the ties as an executive for U.S. oil company Exxon.Tillerson joined a long list of senior officialswho have either resigned or been fired since Trump took office in January 2017.Others include strategist Steve Bannon,national security adviser Michael Flynn,FBI Director James Comey,White House chief of staff Reince Priebus,communications director Anthony Scaramucci,and press secretary Sean Spicer.Recently, staff secretary Rob Porter, communications director Hope Hicksand economic adviser Gary Cohn have resigned from the administration.