Algerian military and police set up checkpoints and sent troops into mountains east of Algiers on Tuesday to look for a Frenchman kidnapped by militants who threatened to execute him over France's intervention in Iraq.
The Caliphate Soldiers, a splinter group linked to Islamic State militants in Iraq and Syria, on Monday published a video claiming responsibility for the abduction and showed a man identifying himself as Herve Gourdel, a tourist from Nice.
Just hours earlier, Islamic State spokesman Abu Muhammad al-Adnani had urged followers to attack citizens of the United States, France and other countries which have joined a coalition to destroy the extremist group.
Islamic State militants have killed two Americans and a Briton kidnapped in Syria, but the capture of the Frenchman was the first claimed by the group's allies outside the large swathe of territory it holds in Iraq and Syria.
Reuters reporters on Tuesday said trucks carrying Algerian special forces headed to the eastern mountains and gendarmerie set up checkpoints not far from the village of Ait Ouabane, where the Frenchman was snatched late on Sunday.
French and Algerian officials and Gourdel's family said the outdoor guide and avid photographer was abducted just days after arriving in Algeria for a hiking holiday in the mountains.
In the video, Gourdel sat between two armed militants who warned Paris they would kill the Frenchman unless France halted its military intervention against Islamic State.
“We will do everything with the coordination of Algerian authorities to ensure he finds his freedom, but obviously in the face of terrorism, which plays on fear and terror, you have to be determined,” French Prime Minister Manuel Valls told Europe 1 radio. “If we pull back by a thumb, we hand them victory.”
“No discussion or negotiations [are possible]. We will not give in to blackmail,” he said.
France on Tuesday urged its nationals to heighten their vigilance in Algeria, citing the kidnapping and French participation in coalition attacks against Islamic State.
Algeria's military fought a brutal war against Islamist militants in the 1990s, and attacks are rarer now in the North African state. But al-Qaida's regional affiliate, Al-Qaida in the Islamic Maghreb, and other groups remain active there.
Gourdel's kidnapping was one of the first abductions of a foreigner by militants in Algeria since the end of that decade-long war that killed around 200,000 people.
At the start of last year, Islamist militants attacked a major gas plant in southern Algeria, killing 40 oil workers, most of them foreigners, during a siege there that was broken by the Algerian armed forces.
The Caliphate Soldiers group earlier this month announced it had broken with al-Qaida in the Islamic Maghreb, known as AQIM, to back Islamic State, in another illustration of its deepening rivalries with Al-Qaida's core leadership.
AQIM central region commander Khaled Abu Suleimane, who claimed leadership of the new group, is originally from and used to operate in the area where the French hostage was taken.
Before the kidnapping, France had managed to reduce the number of its hostages held overseas from 10 to just one.
Gourdel's family and friends said the Frenchman was passionate about nature and photography and had planned to spend around 10 days in Algeria.
Speaking to L'Express newspaper, Gourdel's mother said she had last spoken to him on Sunday. “Everything was going well,” she said. “He told us he was planning two days of trekking and that it would be difficult to get hold of him.”