CAIRO, Aug 12 (Aswat Masriya) - The Islamic State-affiliated Ansar Bayt al-Maqdis purportedly beheaded a Croatian national it has held hostage since last month after an ultimatum set by his abductees was not met, it announced on Wednesday.

The Sinai-based militant group posted a photo of the 30-year-old Croatian national Tomislav Salopek in a washed out orange jumpsuit seemingly after beheading him, in a post shared by its supporters on Twitter.

"The killing of the Croatian captive for his country's participation in the war against Islamic State, after the ultimatum has expired and Egypt's ... government and his country have abandoned him," the caption of the photo read.

Aswat Masriya could not independently verify the authenticity of the photo.

Salopek appeared in a video attributing itself to the media office of Ansar last Wednesday, saying that he will be killed in 48 hours if Muslim women "arrested in Egyptian prisons" are not released.

The ultimatum expired on Friday.

The North Sinai-based Ansar changed its name to Sinai Province after pledging allegiance to Islamic State fighters last November.

The group has increasingly claimed responsibility for attacks in the peninsula, and has claimed at least four attacks in July alone.

The Croatian Foreign Ministry said on July 24, two days after Salopek's abduction that "[the armed men] forced him to get out of the car and drove away with him in an unknown direction."

It said it was doing everything in its power to find information about the kidnapped national.

Salopek worked for a French company in Egypt.

He was married and had two daughters, he said in last week's video.