United Nations Secretary-General Antonio Guterres observes a minute of silence during a wreath-laying ceremony for the 57th anniversary of the death of former Secretary-General Dag Hammarskjold at the UN headquarters in New York, on Sept. 18, 2018. The United Nations on Tuesday marked the 57th anniversary of the death of former Secretary-General Dag Hammarskjold in a plane crash while on a peace mission in Africa. (Xinhua/Li Muzi)