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U.S. National Security Advisor John Bolton (Front) speaks at a press briefing at the White House in Washington D.C., the United States, on Nov. 27, 2018. John Bolton said on Tuesday that U.S. President Donald Trump and Saudi Crown Prince Mohammed bin Salman are not expected to hold a formal bilateral meeting during the Group of 20 (G20) summit in Argentina. (Xinhua/Ting Shen)