Rex Tillerson, who was fired by Donald Trump on Tuesday, said he would be delegating all of his responsibilities as US secretary of state immediately before leaving office at the end of the month. 'What is most important is to ensure an orderly and smooth transition during a time that the country continues to face significant policy and national security challenges,' he said. Trump fired Tillerson after a series of public rifts over policy on North Korea, Russia and Iran, replacing his chief diplomat with the CIA director, Mike Pompeo.