Khashoggi's killing has sparked widespread outrage but Western powers have pledged to maintain close relations with Saudi Arabia, a top oil producer and buyer of U.S. weapons.
Salman, who has recently been accused by the worldwide community for the ordered killing of journalist Jamal Khashoggi and the country's role in the Saudi-led war in Yemen.
All eyes are on Argentina as the most powerful heads of state descend on Buenos Aires for the G20 summit, and Russian President Vladimir Putin and Saudi Crown Prince Mohammad Bin Salman certainly put on a show.
Theresa May used a meeting with the Saudi Crown Prince at the G20 summit to "encourage" him to make sure Saudi Arabia co-operates in the investigation into murdered journalist Jamal Khashoggi.
Bin Salman told Macron not to worry, but Macron replied, "I am anxious".
The meeting with the Crown Prince was Modi's first in a set of "bilaterals" on the sidelines of the G20 that will be followed by meetings with US President Donald Trump and Chinese President Xi Jinping.
The BBC's political editor Laura Kuenssberg wrote on Twitter that 'The Prime Minister stressed the importance of ensuring that those responsible for the appalling murder of Jamal Khashoggi are held to account'.
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Furthermore, the English-language Saudi Gazette shared a video of the meeting reportedly showing a cryptic exchange between the pair on the killing of Khashoggi.
Macron continued the conversation, saying he is "a man of my word".
Mr Macron's office said the meeting with Mohammed bin Salman was justified because European nations wanted to send a united message about the need for probity in the investigation and were not going to sidestep an opportunity to reinforce that message during the G20.
But, in an exclamation point-heavy statement before the summit, Trump said it did not matter whether Prince Mohammed knew about Khashoggi's death because Saudi Arabia was important for USA business and for its hostility to Iran.
However, the US Senate is less enthusiastic about Saudi relations, voting this week to end support for the Saudi coalition in the war in Yemen. But the crown prince's reputation has taken a turn after the murder of Khashoggi in Turkey.
During the course of the day, President Trump "exchanged pleasantries" with Salman, telling reporters that while they didn't talk about hot-button issues concerning the USA and Saudi Arabia, it was possible the pair would do so as the summit rolled on.
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