Isis Tomislav Salopek hostage
Isis hostage Tomislav Salopek is threatened in a ransom videoSITE Intelligence Group

The Sinai Province of the Islamic State (Isis) has claimed to have beheaded a Croatian hostage in Egypt.

The terrorist group posted a picture of dead hostage Tomislav Salopek, with his head cut off on top of his back and wearing a beige jumpsuit similar to the one he had worn in a previous video, according to SITE Intelligence Group.

The employee of geoscience company CGG was abducted on 22 July. A caption on the image said Salopek was killed "for his country's participation in the war against the Islamic State".

The picture of the beheaded Croatian also features screenshots of Egyptian news articles on Croatia's support for Egypt in its war against terrorism and extremism and for the Kurdistan region.

A video released by IS-linked Twitter accounts showed the 30-year-old Croatian wearing a yellow jumpsuit and kneeling beside a masked militant.

In it, the militant makes a threat saying Salopek will be executed if the Egyptian government does not release "Muslim women arrested in Egyptian prisons". The term refers to female Islamist prisoners jailed in a government crackdown following the 2013 military coup that ousted Muslim Brotherhood leader Mohammed Morsi.

Croatian Foreign Affairs Ministry said on Tuesday that it was "using all mechanisms at our disposal" to free the hostage. But last week Isis-linked Twitter accounts posted messages saying they would executed Salopek soon.

The country's prime minister Zoran Milanovic said he will be addressing the nation in couple of hours. President Kolinda Grabar-Kitarovic said in a statement that she is cancelling all her pre-arranged activities for the day

Al-Azhar, the Cairo-based Sunni Muslim world's prestigious religious institute, condemned the killing calling it a "demonic act of which all religions and human traditions are innocent".

Muslim Brotherhood's members in exile said the beheading was a sign that the Egyptian government had failed to curb the rise of extremism in the country.