Britain, France and Germany called on the Saudi and Turkish authorities on Sunday to mount a "credible investigation" into the disappearance of Saudijournalist Jamal Khashoggi, saying they were treating the incident with "the utmost seriousness".

"There needs to be a credible investigation to establish the truth about what happened, and - if relevant - to identify those bearing responsibility for the disappearance of Jamal Khashoggi, and ensure that they are held to account," foreign ministers from the three countries said in a joint statement.

"We encourage joint Saudi-Turkish efforts in that regard, and expect the Saudi Government to provide a complete and detailed response. We have conveyed this message directly to the Saudi authorities," the statement by British foreign minister Jeremy Hunt, France's Jean-Yves Le Drian and Germany's Heiko Maas said.