AP - Police searches and diplomatic efforts intensified over the fate of a Croatian hostage held in Egypt by Islamic State extremists, who threatened to kill him Friday if the government did not release imprisoned Islamist women.

The group's Egyptian affiliate said two days ago it would kill 30-year-old Tomislav Salopek in 48 hours if the Egyptian government did not release jailed "Muslim women" — a reference to those detained in the government's crackdown on supporters of the Muslim Brotherhood and other Islamists.

Salopek, a surveyor in the oil and gas industry working with France's CGG Ardiseis, was abducted in Cairo last month. The demand released Wednesday was entitled "A Message to the Egyptian Government," and it was shot in the style of previous Islamic State propaganda videos in which they threaten and behead hostages. It was the first time such a video had featured a foreign hostage in Egypt.

As extremist sympathizers noted the passage of the deadline on social media, Croatia's foreign minister, Vesna Pusic, met with her Egyptian counterpart in Cairo to press efforts. Foreign Minister Sameh Shourki's office said in statement that he pledged Egypt "will spare no effort" in the search for Salopek.

No other information was immediately available about Salopek, a married father of two. In previous hostage situations involving the Islamic State group (also known as ISIS), deadlines have past and videos of killings have appeared later.

In Croatia, friends gathered in support at Salopek's house in the village of Vrpolje.

"We used to take our children together to school and then sit in the bar across and drink coffee," said Franjo Raspudic, a friend of Salopek. "He never used to talk much about his trips, just that he went places, like Syria or Egypt, and that was the end of it. He is a quiet guy, closed to himself. Straight ace, I would say."

In Egypt, the sister of a woman jailed for alleged ties to the outlawed Brotherhood urged the extremists to spare Salopek. Doaa el-Taweel, sister of jailed photographer and activist Esraa el-Taweel, said that her sister is innocent and that "her release should not come at the expense of another innocent person."

Esraa el-Taweel disappeared in June for weeks before the Interior Ministry announced that they arrested her on charges of belonging to the Brotherhood, which has been declared a terrorist organization, and for spreading false information to tarnish the country's image. She is now awaiting trial.

Croatia's President Kolinda Grabar-Kitarovic said Friday she would talk to Egyptian President Abdel-Fattah al-Sissi about the kidnapping, and that Croatian authorities were doing all in their power to resolve it.

She said she could not go into specifics because of concerns for Salopek's safety and that of "all Croatian citizens who work in places where there is a danger of kidnapping."

A day earlier, Croatian state television said that Salopek's wife, Natasha, flew to Cairo along with the foreign minister.

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 next to Cairo.

The official said Salopek's driver, who the kidnappers left behind, said that the gunmen who seized the Croatian off a western Cairo highway had Bedouin accents.

That suggests they could have come from a variety of isolated places in Egypt, including the restive eastern Sinai Peninsula, where Egypt's ISIS affiliate is based, or the vast western desert that is the gateway to volatile and lawless Libya, home to its own Islamic State branch.

The security official spoke on condition of anonymity because he was not authorized to speak to journalists.

Last December, ISIS' Egyptian affiliate claimed responsibility for the killing of an American oil worker with Texas-based energy company Apache Corp. Apache said that one of its supervisors had been killed in an apparent carjacking in the Western Desert, part of Egypt's mainland, though no video was released of the slaying.

The mother of two other jailed female Islamists also called for Salopek's life to be spared.

"My girls should be released, but not with the blood of innocent people," said Fatma Ahmed, whose daughters, Hind and Rasha Mounir, are appealing life sentences for participating in protests.

Egypt has seen an increase in violence since the 2013 military ouster of Islamist President Mohammed Morsi, with attacks by suspected Islamic extremists in both Sinai and the mainland, focusing primarily on security forces.

In Sinai, the militants have launched increasingly sophisticated attacks in recent months that have killed dozens of Egyptian soldiers and police. Government forces have been carrying out an intensified hunt for them in several northern towns in the peninsula.

Foreign interests have also been targeted, including the Italian Consulate, which was hit with a car bomb last month.

But this is the first time the local ISIS affiliate released a video showing a kidnapped foreigner in Egypt, a major escalation as the country tries to rebuild its crucial tourism industry after years of unrest following the 2011 revolt against autocrat Hosni Mubarak.