The Islamic State group claimed Wednesday to have beheaded a Croatian hostage abducted in Egypt, posting a photo of his decapitated body with his head placed upon his chest on an ISIS-affiliated Twitter account.

The hostage, Tomislav Salopek, had been working as a surveyor in Egypt, for the French geoscience company CGG Ardiseis, when he was abducted from a car last month west of Cairo, according to the BBC.

Upon his capture, the jihadists issued a 48-hour deadline that ended last Friday threatening to kill him if female Muslim prisoners were not released from Egyptian prisons.

A caption that accompanied the picture circulated today, reads in Arabic that Salopek was killed "for his country's participation in the war against the Islamic State," according to the Independent.

The Egyptian interior ministry has been unable to verify the authenticity of the photo, adding that it was still seeking independent confirmation of Salopek's death.

In a similar statement, Christophe Barnini, a spokesman for CGG Ardiseis, stated that the company had been in touch with the Croatian embassy, adding that while the company couldn't confirm Salopek's death on image alone, the company "fear[s] the worst."

The abduction and purported killing were unprecedented in Egypt, which is battling an ISIS insurgency in the eastern Sinai Peninsula, according to the AFP.

The abduction has rattled foreigners working for multinational companies and underscored the jihadists' reach despite a massive military campaign against ISIS.