US Treasury Secretary Steven Mnuchin and UK International Trade Secretary Liam Fox have pulled out of an investment conference in Saudi Arabia.

Their moves come amid allegations the country was behind the killing of Saudi journalist Jamal Khashoggi.

Mr Khashoggi has not been seen since entering the Saudi consulate in Istanbul on 2 October, where Turkish officials allege he was murdered.

Saudi Arabia, which denies the killing, allowed investigators inside overnight.

The Future Investment Initiative summit will take place from 23 to 25 October in the Saudi capital Riyadh.

It is being hosted by Crown Prince Mohamed bin Salman to promote his reform agenda.

His plan for economic and social modernisation, called Vision 2030, aims to reduce Saudi Arabia's dependence on oil and provide new jobs.

As a result, Mr Mnuchin's decision to boycott the summit is seen as a substantial blow to the prince's agenda, correspondents say.

Investment bank Goldman Sachs became the latest business to say it would not send any executives to the conference.

However, a number of major businesses - including Pepsi and EDF - are still intending to go despite growing pressure for a boycott.

Mr Mnuchin announced he would pull out of the summit following a discussion with President Donald Trump and Secretary of State Mike Pompeo. (BBC)