Fears mounted over the fate of a Croatian abducted in Egypt by Islamic State group militants who have threatened to execute him by the end of yesterday.

Croatian President Kolinda Grabar-Kitarovic said she would talk to her Egyptian counterpart President Abdel Fattah al-Sisi by telephone as the jihadist deadline approached.

" Be sure that we are really doing our best to solve this," she was quoted as saying by the state-run HINA news agency.

The unprecedented abduction in the North African country has rattled foreigners who flock to Egypt to work for multinational companies, while underscoring the jihadists' reach

despite a massive military campaign against them.

Although Egypt is fighting an Islamic State group insurgency in the sparsely populated Sinai Peninsula, it had been largely spared the horrific kidnappings conducted by the Islamic State group in Syria, Iraq and Libya.

The father of Tomislav Salopek, who works for the French geoscience company CGG, called on the kidnappers to release the 31-year-old father of two, as Croatian Foreign Minister Vesna Pusic said she was leaving for Cairo to follow the case.

"I am asking the people who hold my son to let him return to his family, because his motive to go to your homeland was exclusively to earn bread for his children.