The United Kingdom, France and Germany on Sunday called for a “credible investigation” into the disappearance of Saudi journalist Jamal Khashoggi.

“Defending freedom of expression and a free press and ensuring the protection of journalists are key priorities for Germany, the United Kingdom and France. In this spirit, light must be shed on [Khashoggi’s] disappearance,” U.K. Foreign Secretary Jeremy Hunt, German Foreign Minister Heiko Maas and French Foreign Minister Jean-Yves Le Drian said in a joint statement.

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The journalist, a U.S. resident who has written for outlets such as The Washington Post, has not been seen since he entered the Saudi consulate in Istanbul earlier this month. Turkish officials suspect he was killed inside the embassy at the direction of Saudi leaders.

The U.K., France and Germany said that they are “treating this 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,” the statement reads.

“We encourage joint Saudi-Turkish efforts in that regard, and expect the Saudi Government to provide a complete and detailed response,” they added. “We have conveyed this message directly to the Saudi authorities.”

President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE has vowed “severe punishment” against Saudi Arabia if the country is found to be behind Khashoggi’s suspected death, but has said that “we don’t know” the necessary details of Khashoggi’s disappearance.

The Saudi government has denied accusations related to its involvement in Khashoggi’s disappearance.