The US has joined other major trading partners in boycotting an upcoming investment conference in Saudi Arabia until the investigation into the disappearance of journalist Jamal Khashoggi is completed. 

US Treasury Secretary Steven Mnuchin, along with high-profile business, government and media leaders from Britain, France, Germany and the Netherlands, are boycotting the Future Investment Initiative in Riyadh, scheduled for October 23-25.

Saudi Arabia will proceed with the high-level summit, dubbed “Davos in the desert”, despite the wave of cancellations.

The decision by Mr Mnuchin to drop out of the conference followed talks with President Donald Trump and Secretary of State Mike Pompeo, who recently returned from meetings with leaders of Saudi Arabia and Turkey.

Just met with @realDonaldTrump and @SecPompeo and we have decided, I will not be participating in the Future Investment Initiative summit in Saudi Arabia.

— Steven Mnuchin (@stevenmnuchin1) October 18, 2018

Mr Pompeo has urged Mr Trump to give Saudi Arabia more time to investigate the disappearance of Mr Khashoggi as Turkish investigators searched the Saudi consulate in Istanbul for a second time in a hunt for clues.

A UK government spokesman for Britain’s International Development Secretary Dr Liam Fox said is was simply not the right time to engage in discussions with Saudi Arabia about financial matters.

The spokesperson said it hoped the investigation into the missing Washington Post columnist who is feared dead after entering the Saudi consulate in Istanbul on October 2, would be “thorough, credible, transparent and prompt”, adding that it encouraged “Turkish-Saudi collaboration and looked forward to the investigation outcome. 

The Washington Post on Friday morning (AEST) published the last column that Mr Khashoggi wrote before traveling to the Saudi consulate where his body is believed to have been dismembered in an interrogation gone wrong.

Mr Khashoggi in a seemingly prophetic article, wrote that citizens of Middle Eastern countries were “either uninformed or misinformed” and warned that Arab governments “have been given free rein to continue silencing the media at an increasing rate”.

French finance minister Bruno Le Maire said the disappearance of Khashoggi was a “serious” matter and the facts about it need to be explained by Saudi authorities.

Dutch foreign minister Stef Blok said that a Dutch trade mission to Saudi Arabia planned for December was also now unlikely to go ahead.

A number of senior top business executives have already cancelled their plans to attend the conference, as has the head of the International Monetary Fund, Christine Lagarde.

Mr Trump met for less than an hour with Mr Pompeo, who gave the President an update on his talks this week with Saudi and Turkish officials about the Khashoggi case.

Referring to the Saudis, Mr Pompeo said he told Mr Trump that “we ought to give them a few more days to complete” their investigation to get a full understanding of what happened.

“I think it’s important for us all to remember, too – we have a long, since 1932, a long strategic relationship with the Kingdom of Saudi Arabia,” he said, calling Saudi Arabia “an important counterterrorism partner”.

Mr Pompeo told reporters he had made clear to the Saudis in his visit to Riyadh that “we take this matter with respect to Mr Khashoggi very seriously”.

-With AAP