Since the jihadists took over Iraq's second city in June 2014, at least 60 journalists, citizen journalists and media workers have fled, according to a report published late yesterday by Reporters Without Borders (RSF).
The study, which described Mosul as a "death trap for journalists", was researched by RSF's partner organisation in Iraq, the Journalistic Freedoms Observatory.
RSF said the IS group, for which Mosul is the largest hub, has not only hunted journalists down but also taken over the city's existing media infrastructure.
The report said it was thanks to the technology seized from local TV studios that IS was able to shoot and broadcast the first, and to this date last, public appearance of its self-proclaimed "caliph" Abu Bakr al-Baghdadi in June last year.
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It said it used the cameras of Sama Mosul TV, which was owned by former Nineveh governor Atheel al-Nujaifi, to shoot the sermon.
Very little information has come out of Mosul other than the group's own propaganda.
Some of the 13 executed journalists' bodies were handed over to the families but in some other cases it took weeks or months to confirm the death.
Anyone with friends or relatives still in Mosul is afraid to talk, turning Mosul into what the report called an "information black hole".
The report included short biographies of the 13 executed journalists and said the fate of at least 10 journalists who are thought to still be held by IS remained unclear.