ISTANBUL (AP) — Turkish investigators believe a prominent Saudi journalist who contributed to The Washington Post was killed in "a preplanned murder" at the kingdom's consulate in Istanbul, the Post reported Saturday night, citing two anonymous officials.

Saudi authorities called the allegation "baseless."

One Turkish official also told The Associated Press that detectives' "initial assessment" was that Jamal Khashoggi was killed at the consulate, without elaborating.

Khashoggi, who has lived in self-imposed exile in the U.S. for the last year, vanished Tuesday while on a visit to the consulat...