London, Oct 14: Britain and the US are considering boycotting a major international conference in Saudi Arabia after the disappearance of Saudi journalist Jamal Khashoggi, the BBC reported on Sunday.Khashoggi, a critic of the Saudi government, vanished on October 2 after visiting its consulate in Istanbul, triggering tensions between Riyadh and Ankara.The authorities in Istanbul believe he was murdered there by Saudi agents. Saudi Arabia has rejected the allegations as "lies".Several sponsors and media groups have decided to pull out of this month's investment conference in Riyadh, dubbed Davos in the Desert, as a result of concerns over Khashoggi's fate.Diplomatic sources have now told the BBC that both US Treasury Secretary Steve Mnuchin and UK International Trade Secretary Liam Fox might not attend the event, being hosted by the kingdom's Crown Prince Mohamed bin Salman to promote his reform agenda.A spokesman for the UK's international trade department said Fox's diary was not yet finalized.A joint statement of condemnation, if it is confirmed that Khashoggi was killed by Saudi agents, was also being discussed by US and European diplomats, the BBC said.However, Khashoggi's fiancée Hatice Cengiz has said that words alone won't be good enough if he has been murdered."If we have already lost Jamal, then condemnation is not enough," she wrote in a piece for the New York Times. "The people who took him from us, irrespective of their political positions, must be held accountable and punished to the full extent of the law."US President Donald Trump has said the US would inflict "severe punishment" on Saudi Arabia if the kingdom was found to be responsible for the death of Khashoggi, a contributor to the Washington Post.Turkish Foreign Minister Mevut Cavusoglu said Saudi Arabia was not yet co-operating with the investigation despite a statement from Saudi Interior Minister Prince Abdulaziz bin Saud bin Naif bin Abdulaziz saying his nation wanted to uncover "the whole truth", the BBC said.Cavusoglu has urged the kingdom to allow Turkish officials to enter the consulate.