Jamal Khashoggi has not been seen since October 2 when he went to the Saudi consulate in Istanbul to obtain official documents for his upcoming marriage.
Britain's foreign secretary on Thursday warned that Saudi Arabia faces "serious consequences" if the suspicions of Turkish officials that journalist Jamal Khashoggi was murdered after entering the Saudi consulate in Istanbul turn out to be true.
"People who have long thought of themselves as Saudi's friends are saying this is a very, very serious matter.
"If these allegations are true, there will be serious consequences because our friendships and our partnerships are based on shared values," Jeremy Hunt told AFP.
Hunt said he had spoken to Saudi Foreign Minister Adel al-Jubeir and had told him "how very, very concerned the United Kingdom is".
Turkish President Recep Tayyip Erdogan has urged Saudi Arabia to release footage of Khashoggi and President Donald Trump has demanded answers over his fate, as the kingdom faces growing pressure to provide a convincing explanation for his disappearance.
The Washington Post, the daily to which Khashoggi was a contributor, added to the mystery by reporting Saudi Crown Prince Mohammed bin Salman had ordered an operation to "lure" the critical journalist back home.
Khashoggi has not been seen since October 2 when he went to the Saudi consulate in Istanbul to obtain official documents for his upcoming marriage. Turkish officials quoted in media have said he was killed but Riyadh denies that.
The mystery has captivated the world but also threatens to harm brittle Turkish-Saudi relations and hurt efforts by the crown prince to improve the image of his country with a reform drive.