A French hostage has been beheaded in a video released by an Algerian group linked to Islamic State.
Herve Gourdel, a 55-year-old hiker from Nice in southern France, was kidnapped on Sunday by Jund al Khilifa.
The group had given France a 24-hour deadline to stop its airstrikes against IS in Iraq.
French president Francois Hollande confirmed the video was genuine and denounced the killing as "cruel and cowardly".
He added that he will be chairing a special security meeting at the Elysee Palace on Thursday.
In the clip issued by Algerian militants, the tourist was seen kneeling with his arms bound behind his back, as four masked men read a message in Arabic condemning France.
Mr Gourdel was then pushed on to his side and held down.
Shortly after the group - known as the Caliphate Soldiers in English - released the video, French foreign minister Laurent Fabius insisted the abduction would not deter his nation's participation in a US-led offensive against IS.
The video was entitled A Message With Blood To The French Government, and began to circulate on jihadist websites on Wednesday.
It began with an excerpt of Mr Hollande making a speech, before showing Mr Gourdel in his final moments of life.
Prior to the mountain guide's beheading, Mr Hollande had insisted: "As grave as this situation is, we will not give in to any blackmail, any pressure, any ultimatum, no matter how odious, how despicable."
In a statement before news of the killing emerged, Mr Gourdel's family said they had learned of the kidnapping "with great pain", and described him as a "father, partner, son, brother and very dear friend".
Intelligence sources believe there could be 10 Western hostages still being held by Islamic State.
One Briton, David Haines, and Americans James Foley and Steven Sotloff, have been killed by the group in the past few weeks.
Islamic State has threatened to kill Alan Henning, a British aid convoy volunteer.
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