In a stunning development that will leave an already depleted U.S. diplomatic corps in even further disarray, the State Department's top diplomat in charge of North Korea policy has announced that he will step down from his post at the end of the week.

"Ambassador Joe Yun, a respected member of the Senior Foreign Service, has decided to retire for personal reasons," State Department spokeswoman Heather Nauert said in an email to The Japan Times, adding that Secretary of State Rex Tillerson had "reluctantly accepted his decision and wished him well."

"Ambassador Yun has served with distinction for more than 30 years, most recently as Special Representative for North Korean Policy and prior to that as U.S. Ambassador to Malaysia," Nauert said.