Watchers were left without this crucial morsel of body language right after Trump announced he would not meet Putin officially, as he had planned to, citing the recent Russia-Ukraine navy scuffle off the Crimean shores.
Meanwhile Russian President Vladimir Putin and Prince Mohammed shared a smiley, enthusiastic greeting at the gathering.
May's office says the prime minister stressed to Salman the importance of ensuring those responsible for the "appalling murder" of Khashoggi are held to account.
Khashoggi, a United States resident who wrote for The Washington Post and had been critical of Prince Mohammed, was lured to the Saudi consulate in Istanbul to get marriage documents on October 2, where he was killed and reportedly dismembered. Riyadh has long sought to distance the crown prince from the incident, despite increasing evidence directly linking him to it.
At center stage was Argentine President Mauricio Macri, hosting this year's summit of G20 industrialized nations.
On Saturday, the Wall Street Journal reported that according to the CIA, Prince Mohammed "sent at least 11 messages to his closest adviser, who oversaw the team that killed ..."
Police, coast guard and border patrol officers roped off a 12-square-kilometer (5-square-mile) area near the Buenos Aires convention center, where the summit is taking place.
Prime Minister of Japan Shinzo Abe and his wife Akie arrive at Ministro Pistarini International Airport.
Prime Minister Justin Trudeau says he asked Russian President Vladimir Putin to release Ukrainian sailors who have been taken prisoner.
Xi met the prince on the sidelines of the G20 summit in Buenos Aires on Friday and said China would support the kingdom's economic development, adding that stability was the cornerstone for prosperity and progress in the Gulf.
After vehement denials that Riyadh was involved in Khashoggi's disappearance, Saudi officials admitted that the USA -based dissident was killed inside the embassy building in what it called a "rogue" operation.
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