WASHINGTON - Fired US Secretary of State Rex Tillerson plans to speak soon with CIA Director Mike Pompeo, who has been nominated to succeed him, the State Department said on Thursday.Spokeswoman Heather Nauert said Tillerson had handed over the day-to-day responsibilities of running the department to Deputy Secretary John Sullivan, but would continue to work from his office and retain the title of secretary of state until his departure at midnight on March 31.President Donald Trump fired Tillerson on Tuesday after a series of rifts over policy on North Korea, Russia and Iran, publicly announcing the decision on Twitter just hours after the top U.S. diplomat returned early from a trip to Africa.Differences over how to deal with North Korea's development of nuclear-tipped missiles capable of hitting the United States was a main factor in Trump's decision, sources familiar with the deliberations told Reuters."The secretary is in the building today ...," Nauert told reporters. "He has ongoing meetings and business to attend to wrapping up his term here at the State Department."Pompeo has to be confirmed by the U.S. Senate before he can succeed Tillerson. The Senate Foreign Relations Committee was not expected to hold hearings on the CIA director's nomination until April, after Tillerson has left the State Department.