Cengiz wrote that she was "confident in the abilities of Turkish government officials." "At this time, I implore President Trump and first lady Melania Trump to help shed light on Jamal's disappearance," she said.
Riyadh has said Khashoggi left the consulate after his visit.
Although Khashoggi knew that his opinions had angered certain people, he entered the consulate "without doubting he would be safe there," his fiancee wrote, but after three hours of waiting "fear and concern" overcame her.
Khashoggi had fled his homeland in September last year and had been living in self-imposed exile in the United States, where he had applied for US citizenship, Cengiz said.
A former Saudi government advisor, Khashoggi has been openly critical of Prince Mohammed, accusing him of introducing a new era of "fear, intimidation, arrests and public shaming." Cengiz wrote she remains confident that the "great man" is still alive, "although my hope slowly fades away each passing day.
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