Egyptian foreign minister Sameh Shoukry said his country could not confirm that a Croatian national abducted by an Islamic State affiliate in Egypt had been murdered, after an image of a decapitated body circulated online Wednesday.
Shoukry said during a phone conversation with his Croatian counterpart, Vesna Pusic, that "Egyptian authorities have not received confirmation" of the purported decapitation of Tomislav Salopek.
He added that authorities are "doing their utmost to catch the culprits."
The 31-year-old father of two was abducted last month west of Cairo.
The militants threatened to kill him if female Muslim prisoners were not released from Egyptian jails within 48 hours, a deadline which expired on Friday.
Salopek is the second foreign captive to have been purportedly killed by the north Sinai-based jihadist faction, which announced its allegiance to the Islamic State (IS) group in November.
The first victim was US oil worker William Henderson, who was killed in late December.
The still picture, posted on IS-affiliated Twitter accounts, claims to show the decapitated body of Salopek with his head placed on his back and the signature black flag of IS planted in the sand nearby. The photo carried a caption in Arabic that said Salopek was killed for "his country's participation in the war on the Islamic State and the deadline (to release the prisoners) had expired.”
The Croatian foreign minister had visited Cairo last Thursday in an attempt to find a way to end Salopek's ordeal.
The Egyptian government had publicly said it was doing its best to secure Salopek's release.
Egypt's foreign minister said authorities are now working to verify the authenticity of the circulated photo.
Egypt's Al-Azhar, the highest institute of learning in Sunni Islam, has condemned the killing of Salopek, calling it a "satanic action" contrary to all religions and traditions.
Germany condemned the purported slaying as an "abhorrent act" and France called it a "despicable assassination."
Egypt has been fighting an increasing Islamist insurgency that is spearheaded by Sinai Province, the country's most lethal militant faction.
Formerly known as Ansar Beit Al-Maqdis, the group was designated a terrorist organization in 2014 by the Egyptian government.
Although the group has killed hundreds of police officers and military personnel, foreigners have largely been spared from the violence.
Despite a sweeping crackdown by authorities, the group has managed to stage attacks in mainland cities, including Cairo.
Last month, the group claimed responsibility for a car bomb, which targeted the Italian consulate in Cairo and killed one civilian, the first such attack against a foreign mission in the country.