August 12, 2015 7:37 AM EDT

A photograph believed to be from the Egyptian branch of the Islamic State in Iraq and Syria (ISIS) shows what looks like the beheading of a man the group threatened to execute earlier this month.

Last week, a video believed to be from ISIS in the Sinai peninsula threatened to kill a man who identified himself as 30-year-old Tomislav Salopek if the Egyptian government did not release female Muslim hostages within 48 hours. It was unclear exactly whose release the group was calling for. The video was circulated by ISIS supporters and shot in a style similar to other ISIS videos, the AP reports.

Salopek, a married father of two, worked as a topographer for the French geoscience company CGG and was captured on July 22. Croatia’s Foreign Ministry confirmed last month that a Croatian national with the same initials as Salopek was kidnapped in Cairo.

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