This image made from a militant video posted on a social media site on Aug. 5 purports to show a militant standing next to hostage Tomislav Salopek of Croatia. The group now claims it has beheaded Salopek. (Uncredited/AP)

An Islamic State affiliate claimed Wednesday to have beheaded a Croatian national held hostage for weeks in what would be the group’s first killing of a foreign captive in Egypt.

If confirmed, the death would mark a fresh challenge to Egypt’s economy and the country’s effort to stem a rising Islamist insurgency that has targeted major tourist sites and military outposts.

The Croatian hostage, Tomislav Salopek, worked for a French geoscience company in Egypt, which depends on many foreign firms for construction and other major projects.

A purported photo of Salopek’s decapitated body was posted Wednesday by an Islamic State-linked Twitter account. The caption said Salopek was killed because of his country’s “war” on the Islamic State but gave no further details.

Croatia has not contributed forces to operations against the Islamic State, but the State Department has said that the Balkan nation has provided unspecified military supplies.

In Zagreb, Croatian Prime Minister Zoran Milanovic said that he could not immediately confirm the claims of the killing but noted that “what we see looks horrific.” Egypt’s Foreign Ministry could not be reached for comment.

Salopek, 30, was abducted on a desert road outside Cairo as he drove to work on July 22, the Croatian government said.

Two weeks later, he appeared in a video posted online by a group that calls itself the Sinai Province of the Islamic State. Salopek read a statement saying he would be killed within 48 hours unless the Egyptian government released all female Muslim prisoners.

His abduction so close to Cairo has raised concerns about security in the capital and the safety of the thousands of foreign nationals who live and work there.

Insurgents have largely targeted security forces outside Cairo in their years-long campaign against the Western-allied government. Militants stepped up their attacks after Islamist President Mohamed Morsi was ousted in a military coup in 2013.

But Cairo is now in the extremists’ crosshairs.

Map: What a year of Islamic State terror looks like

In June, a car bombing in the city killed Egypt’s top prosecutor. A few days later, a car bomb exploded outside the Italian Consulate in central Cairo, killing one person.

The increase in violence undermines the government’s efforts to portray Egypt as an investment-friendly country. The Egyptian economy has been plagued by slow growth since the upheavals of the Arab Spring.

Last week, President Abdel Fatah al-Sissi inaugurated a new section of the Suez Canal, declaring the project part of Egypt’s broader war against terrorism. Salopek’s killing is likely to prompt foreign companies to undertake stricter security measures.

Salopek’s abduction “reveals the weakness of our security force in being able to prevent things like this,” said Hisham Kassem, a Cairo-based political analyst.

The kidnapping “will raise insurance prices for products and people coming to work here,” Kassem said. “And this will have an economic effect.”

The Islamic State-linked Sinai faction has stepped up attacks on a range of targets in recent months. A video in July purported to show a rocket or missile damaging an Egyptian naval vessel off the Sinai.

In June, militants with explosives and weapons tried to storm the ancient temple of Karnak in Luxor, a major tourist site about 300 miles south of Cairo. There was no assertion of responsibility, but suspicion fell on factions linked to the Islamic State.

In early 2014, a suicide bomber struck a bus carrying foreign tourists in Taba, a popular beach destination on the Sinai near the Israeli border. The Sinai-based Ansar Bayt al-Maqdis, a militant group that has since pledged allegiance to the Islamic State, claimed responsibility for that attack.

Other cells linked to the Islamic State have carried out beheadings of foreign captives elsewhere in the region for more than a year, including Western journalists and a group of Egyptian Christians working in Libya.

Heba Habib in Cairo and Brian Murphy in Washington contributed to this report.

Read more:

Map: The world according to the Islamic State

What a year of Islamic State terror looks like