Fighters linked to the Islamic State in Iraq and the Levant (ISIL) group have said they beheaded a Frenchman abducted in Algeria, after giving a 24-hour deadline to Paris.

Herve Gourdel, a 55-year-old hiker from the southern French city of Nice, was kidnapped on Sunday by Jund al-Khalifa, which demanded France stop its air strikes against ISIL in Iraq.

US terrorism watchdog SITE Intelligence Group said Jund al-Khilafah armed group released a video online purporting to show the beheading on Wednesday.

The French government would not immediately comment.

The latest footage came two days after Jund al-Khilafa group released a video showing Gourdel pleeing to his government not to intervene in Iraq.

"I am in the hands of Jund al-Khilifa. This group is asking me to ask you [President Francois Hollande] to not intervene in Iraq. I ask you to do everything to get me out of this bad situation and I thank you."

France launched its first air attacks on ISIL fighters last week, after joining a US-led coalition to "degrade and destroy" the threat posed by the group.

The French foreign ministry and presidency acknowledged Gourdel had been abducted, and that the video was genuine.

"We will do everything we can to liberate hostages," said France's foreign minister Laurent Fabius. "But a terrorist group cannot change France's position."

Jund al-Khalifa, or "the soldiers of the caliph", are believed to have broken away from the local al-Qaeda affiliate and pledged alliegence to ISIL.

The abduction was announced on the same day ISIL's spokesman, Abu Mohammed al-Adnani, called on supporters to attack foreigners wherever they are.

Al Jazeera