CAIRO, Egypt (AP) — Islamic State sympathisers circulated an image yesterday that appears to show the grisly aftermath of the beheading of a Croatian hostage abducted in Egypt, which if confirmed would mark the first such killing of a foreign captive in the country since the extremist group established a branch here last year.

The killing of the 30-year-old oil and gas sector surveyor likely will rattle companies with expatriate workers in Egypt and cast a cloud over President Abdel-Fattah el-Sissi’s attempts to boost international investment and tourism following years of unrest.

The still image, shared by IS supporters on social media, appeared to show the body of Tomislav Salopek, a married father of two, wearing a beige jumpsuit resembling the one he had worn in a previous video. A black flag used by the Islamic State and a knife were planted in the sand next to him.

The photo carried a caption in Arabic that said Salopek was killed “for his country’s participation in the war against the Islamic State,” and after a deadline had passed for the Egyptian government to meet his captors’ demands.

The picture also contained an inset of two Egyptian newspaper reports, with one headline declaring Croatia’s support for Egypt in its war against terrorism and another saying Croatia reiterated its support for the Kurds, who have been battling the IS group in Syria and Iraq. Croatian troops fought in the US-led coalition in Iraq and still serve in the NATO-led force in Afghanistan.

In a televised address to the nation, Croatian Prime Minister Zoran Milanovic said authorities there could not confirm the killing with certainty.

“We cannot 100 percent confirm it is true, but what we see looks horrific. A confirmation may not come for several days,” he said, appealing for calm and adding that officials will not stop searching for Salopek as long as there is any hope.

The Egyptian Foreign Ministry had no immediate comment.

Al-Azhar, the Sunni Muslim world’s prestigious religious institute, condemned the apparent killing, calling it a “demonic act of which all religions and human traditions are innocent.” The statement also said Islamic law stipulates that it is forbidden to shed the blood of foreigners.

Exiled members of the Muslim Brotherhood group, branded a terrorist organisation by authorities, said the beheading was a sign that the government had failed to curb the rise of extremism in the country.

The Associated Press could not independently verify the image. However, it bore markings consistent with a filmed hostage demand released last week by the group, which calls itself the Sinai Province of the Islamic State. It was not clear where the video was shot.

In that video, the IS affiliate set an Aug. 7 deadline for Egyptian authorities to free “Muslim women,” a term referring to female Islamist prisoners detained in a sweeping government crackdown following the 2013 military ouster of the country’s Islamist president.

The extremists’ videotaped demand was entitled “A Message to the Egyptian Government,” and was shot in the style of previous IS propaganda videos. It came just a day before el-Sissi hosted a much-hyped ceremony with foreign dignitaries to mark the opening of a new section of the Suez Canal.

As the deadline expired Friday, an Egyptian security official said that security forces were searching for Salopek across the country, focusing on the western provinces of Matrouh and Wadi Gedid, which border Libya, as well as Beheira in the Nile Delta and Giza, part of greater Cairo.

Speaking on condition of anonymity because he wasn’t authorised to talk to journalists, the official said Salopek’s driver, left behind by the kidnappers, said that the gunmen who seized the Croat on a highway just west of Cairo had Bedouin accents.

That suggests they could have come from a variety of isolated places in Egypt, including the restive northern Sinai Peninsula, where Egypt’s Islamic State affiliate is based, or the vast Western Desert, which is a gateway to volatile and lawless Libya, home to its own Islamic State branch.

The sister of a woman jailed on charges of belonging to the Brotherhood, Esraa el-Taweel, who had previously pleaded for Salopek’s life to be spared, said she spoke about the matter during a recent prison visit.

“She rejected that the life of an innocent man who is not responsible for other detainees be negotiated,” said Doaa el-Taweel, who asserts that her sister is innocent. “She rejected the whole thing.”

Salopek, a surveyor working with France’s CGG Ardiseis, was abducted on July 22. The company has an office in the leafy southern suburb of Maadi, where many expats and diplomats live.

Last week, Croatian Foreign Minister Vesna Pusic met with her Egyptian counterpart in Cairo to press for Salopek’s release, while Egyptian Foreign Minister Sameh Shoukry’s office pledged in statement that Egypt would ” spare no effort” in the search for him.

The Islamic State group holds about a third of Iraq and neighboring Syria in its self-declared “caliphate.” In Syria, IS militants have killed foreign journalists and aid workers, starting with American journalist James Foley in August last year, and released grisly videos of the beheadings.

Foley’s taped beheading was followed by the killing of American-Israeli journalist Steven Sotloff, British aid workers David Haines and Alan Henning, American aid worker Peter Kassig, as well as Japanese nationals Haruna Yukawa and Kenji Goto.

In Libya, an IS affiliate released a video in February showing its fighters beheading a group of Coptic Christians from Egypt. In April, another video showed them beheading and shooting dead groups of Ethiopian Christians.

Egypt has seen an increase in violence since the ouster of Islamist President Mohammed Morsi, with attacks by suspected Islamic extremists in both the Sinai Peninsula and the mainland focusing primarily on security forces.

Militants have also targeted foreign interests, including the Italian Consulate, which was hit with a car bomb last month. That came just days after another bomb killed Prosecutor General Hisham Barakat in an upscale Cairo neighbourhood.

But this would be the first time the local Islamic State affiliate has captured and then killed a foreigner in Egypt, a major escalation as the country tries to rebuild its crucial tourism industry after years of unrest following the 2011 revolt that toppled autocrat Hosni Mubarak.

Last December, the affiliate claimed responsibility for the killing of an American oil worker with Texas-based energy company Apache Corp. Apache had said that previous August that one of its supervisors had been killed in an apparent carjacking in the Western Desert.