The Islamic State has released a video claiming to show the beheading of British captive David Haines.
The father-of-two, an aid worker, was abducted by militants in Syria last year.
In the video, which has been posted on sites such as YouTube, the extremists also threaten to execute another Briton.
Islamic State (IS) extremists had threatened to kill Mr Haines and have not responded to any of the family’s attempts to make contact so far, the Foreign and Commonwealth Office (FCO) said.
Militants from IS have beheaded two American journalists, posting the evidence online in gruesome videos featuring a masked jihadist with a British accent. The other was James Foley.
Mr Haines, 44, was taken while working for relief agency ACTED in Syria in March 2013, having previously helped local people in Libya and South Sudan.
He had been working for the French aid agency for just ten days when he was taken alongside Federico Motka, an Italian-Swiss aid worker freed four months ago after a ransom was paid.
The 44-year-old has a teenage daughter in Scotland from a previous marriage with wife Louise and a four-year-old daughter in Croatia from his present marriage.
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