Theresa May has confronted the Saudi crown prince over Jamal Khashoggi’s murder, telling him he must take action to ensure “such a deplorable incident” does not happen again.
The prime minister told Mohammed bin Salman there needed to “be full transparency about exactly what had happened” and also full cooperation with Turkish authorities.
Mrs May had a meeting with the prince on the first day of the G20 summit of world leaders in Buenos Aires, Argentina.
A Downing Street statement said: “The prime minister stressed the importance of ensuring that those responsible for the appalling murder of Jamal Khashoggi are held to account, and that Saudi Arabia takes action to build confidence that such a deplorable incident could not happen again.”
Mr Khashoggi, a journalist and critic of the Saudi regime, was murdered last month when he went into the country’s consulate in Istanbul.
The CIA has reportedly concluded that the crown prince ordered the killing – a claim strongly denied by the Saudis.
After changing their explanation several times, Saudi authorities say he was given a lethal injection and then dismembered in a botched operation to get him back to the country.
Five of the “hit squad” who flew into Turkey are facing the death penalty.
Mrs May also used her meeting to urge the prince to quickly end the war in Yemen – a conflict which has caused a devastating famine.
Weapons supplied by the UK to the Saudis have been used in the fighting.
However, Number 10’s statement said the PM also “reiterated UK support for Saudi Arabia’s security, including the very real threats posed by Iranian interference in Yemen”.
G20 leaders had earlier largely blanked the crown prince as they gathered for the “family photo” – apart from Russian President Vladimir Putin, who greeted the prince enthusiastically with a high-five and smiles.
French President Emmanuel Macron was also filmed speaking to the prince on the sidelines of the summit.
Cameras picked up fragments of their words, including Mr Macron apparently telling him: “I am worried… I told you… You never listen to me…”
The subject of their conversation was unclear however.
Saudi-owned TV station Al Arabiya said there had been a friendly meeting between Donald Trump and the crown prince.
However, a White House official said the US president had so far only exchanged pleasantries with him.
Tensions at the summit were also simmering over Russia’s actions in Ukraine, where Russian guards earlier this week fired on and captured three Ukrainian ships in the Black Sea.
Mr Trump cancelled his meeting with Mr Putin and G7 foreign ministers put out a strong statement expressing their “utmost concern”.
The statement reiterated support for Ukraine and added “we do not, and will never, recognise Russia’s illegal annexation of the Crimean peninsula”.
Mr Trump’s key agenda item though, will be Saturday’s dinner with Chinese President Xi Jinping – a head to head that world markets will also be watching closely.
The world’s two biggest economies have imposed tariffs on hundreds of billions of dollars of each other’s imports.
Beijing is hoping to Mr Trump will back down from plans to increase tariffs from 10% to 25% in January.