New Isis hostage video: Croatian threatened with execution 'in 48 hours'

Gunmen shown threatening to kill the hostage if Egyptian authorities do not release 'Muslim women' they hold in prison

Nato's Dr Jamie Shea says Isis is splitting into two groups: one focused on the caliphate and the other on attacking the West

The Isis militant group has reportedly released a video threatening to kill a Croatian hostage within 48 hours unless Egypt releases "Muslim women" from jail.

The video showed a man in a yellow jumpsuit kneeling before a masked militant wielding a knife.

The flag of the terrorist group flutters next to him, and the video says it comes from Isis's Egyptian affiliate group in the Sinai Peninsula.

Reading from a note, the man identifies himself as 30-year-old Tomislav Salopek and says he was captured by Isis on 22 July.

He said he will be killed if Egyptian authorities do not give in to the demands, although it is not clear exactly who the group want released from prison.

The authenticity of the video has not yet been solidly verified, but bears resemblance to previous hostage videos released by the group, and has been shared widely by the group's supporters online.

The video could not have come at a worse time for the Egyptian government, who are currently preparing to inaugurate an $8.5 billion extension to the Suez Canal on 6 August, a huge project that is the centrepiece of President Abdel Fattah al-Sisi's plans to revitalise the country's economy.

The release of the video came as Egypt plans to officially open a huge new extension to the Suez Canal (STRINGER/Reuters)

Egypt holds thousands of Islamists and suspected Muslim Brotherhood supporters in prison, following the overthrow of former President Mohammed Morsi in 2013.

Last month, Croatia's Foreign Ministry had said that one of its nationals, with the same initials as as Salopek, had been kidnapped in Cairo on their way to work.

Mr Salopek said he worked for CGG Ardiseis, a French oil and gas company, that has an office in a Cairo suburb that is home to many expats.

Neither CCG or the Egyptian authorities were available for comment.