Croatian hostage

The group's Egyptian affiliate said two days ago it would kill 30-year-old Tomislav Salopek in 48 hours if the Egyptian government did not release jailed "Muslim women" — a reference to those detained in the government's crackdown on supporters of the Muslim Brotherhood and other Islamists.

Salopek, a surveyor in the oil and gas industry working with France's CGG Ardiseis, was abducted in Cairo last month. 

The group had earlier said it would do so in the coming hours if the Egyptian government does not release jailed "Muslim women."

Doaa el-Taweel, sister of jailed photographer and activist Esraa el-Taweel, said on Friday that her sister is innocent but that "her release should not come at the expense of another innocent person."

The threat came a day before the country plans to unveil a highly promoted new extension of the Suez Canal.

The video, circulated on social media by Islamic State sympathizers, shows a man wearing a yellow jumpsuit kneeling in the desert before a knife-wielding masked man in military fatigues.