Egypt's foreign minister says authorities are still working to verify the authenticity of a photo circulated by Islamic State group supporters that appears to show the grisly aftermath of the beheading of a Croatian hostage.

Foreign Minister Sameh Shoukry told Al-Arabiya television late Wednesday that the "relevant authorities must first confirm the authenticity of the image that was circulated of the killing of the Croatian citizen."

He added that "these terrorist operations target citizens of different nationalities in a number of countries in the region and the world."

His remarks were posted on the Foreign Ministry's Facebook account.

Egypt's IS-affiliated militant group announced on Wednesday that it has killed Croatian hostage Tomislav Salopek.

Ansar Beit Al-Maqdis published a graphic photo showing the victim's decapitated body on IS-affiliated Twitter accounts Wednesday afternoon.

The militant organisation gave the Egyptian government a 48-hour deadline on Wednesday threatening to kill Salopek if "Muslim women prisoners" in Egyptian jails are not released.

The deadline expired on Friday.