The Islamic State group's radio station says its Egyptian affiliate killed a Croatian hostage, the first word from the extremist group a day after a gruesome image of his beheading circulated online.

Al-Bayan radio station said Thursday that "soldiers of the Caliphate" killed Tomislav Salopek, "whose country is participating in the war against the Islamic State."

It said the killing came after a deadline passed for "the renegade Egyptian government" to meet his captors' demands to free jailed Islamist women.

Salopek's killing is the first of a foreign captive in Egypt, where the government has been struggling to project an image of stability and revive the economy following years of unrest.

Croatian officials said Wednesday that authorities could not confirm the killing with certainty.