RABAT: Algerian extremists allied with the Islamic State group have decapitated a French hostage after France ignored their demand to stop airstrikes in Iraq, according to a video obtained Wednesday by a US-based terrorism watchdog.

A group calling itself Jund al-Khilafah, or Soldiers of the Caliphate, had said they would kill French mountaineer Herve Gourdel after abducting him Sunday unless France ended its airstrikes against Islamic State fighters in Iraq within 24 hours.

The French government insisted it would not back down.

In the video, masked gunmen from the newly formed group that split away from al Qaeda's North Africa branch, pledged their allegiance to the leader of the Islamic State group, Abu Bakr al-Baghdadi, and said they were fighting his enemies.

They criticised the French attacks in Iraq as well as its intervention against radical Islamists in Mali.

Terrorism watchdog SITE Intelligence Group said the video had been posted on social networking site Twitter. Gourdel – a 55-year-old mountaineering guide from Nice – was seized in the Djura Djura mountains of northern Algeria on Sunday during a hiking trip. His Algerian companions were released.

Algerian forces unleashed a massive search for him in the remote mountainous region that is one of the last strongholds of Islamic extremists in Algeria.

The video resembled those showing the beheadings of two American journalists and a British aid worker in recent weeks, but instead of starting with clips of President Barack Obama speaking, it showed French President Francois Hollande.

France started airstrikes in Iraq on Friday, the first country to join the US military campaign against the Islamic State fighters there. “Our values are at stake,” French Prime Minister Manuel Valls said Wednesday after hearing about the video.

He would not comment further, but minutes earlier he insisted that France would continue fighting in Iraq as long as necessary.

Algeria has been fighting the extremists since the 1990s and in recent years they had been largely confined to a few mountainous areas, where they have concentrated on attacking soldiers and police while leaving civilians alone.

The killing of a hostage represents a departure for militant groups in Algeria which in the past decade have made millions of ransoming hostages.

The new group split away from al Qaeda's North Africa branch and declared allegiance to the al-Baghdadi's group in Iraq and Syria and has apparently adopted their tactic of killing hostages.