Holding a picture of missing Saudi writer Jamal Khashoggi, Tawakkol Karman, of Yemen the Nobel Peace Prize laureate for 2011, talks to members of the media near the Saudi Arabia consulate in Istanbul. Picture: Emrah Gurel/AP

Istanbul — Turkey's official news agency says prosecutors are extending an investigation into the disappearance of a veteran Saudi journalist.

Anadolu news agency said Saturday the Istanbul public prosecutor's office began a probe into Jamal Khashoggi's disappearance Tuesday, immediately after he went missing. It said the investigation over allegations that the writer was detained had "deepened."

Khashoggi, 59, went missing while on a visit to the consulate in Istanbul for paperwork to marry his Turkish fiancée. The consulate insists the writer left its premises, contradicting Turkish officials who say they believe he is still there.

Khashoggi has written columns for the Washington Post critical of Saudi Arabia's assertive Crown Prince Mohammed bin Salman.