
U.S. Secretary of Defense James Mattis (L) and Ukrainian President Petro Poroshenko stand during a welcome ceremony at the Pentagon in Washington D.C., the United States, on June 20, 2017. (Xinhua/Ting Shen)

U.S. Secretary of Defense James Mattis (L) and Ukrainian President Petro Poroshenko stand during a welcome ceremony at the Pentagon in Washington D.C., the United States, on June 20, 2017. (Xinhua/Ting Shen)