Islamic State video shows British hostage David Haines being beheaded
Haines was abducted in Syria in 2013 while working for an international aid agency
BEIRUT(Syria): Islamic State extremists have released a video purportedly showing the beheading of British aid worker David Haines, who went missing in Syria last year.
The video emerged a day after the family of Haines issued a public plea late Friday urging his captors to contact them.
The British Foreign Office said late Saturday that it was "working urgently to verify" the video.
"If true, this is another disgusting murder," the Foreign Office said in a statement. We are offering the family every support possible. They ask to be left alone at this time."
Islamic State militants have beheaded two American journalists, James Foley and Steven Sotloff, as well as Kurdish and Lebanese fighters, and posted video evidence online.
At the end of the last video showing the beheading of American journalist Steven Sotloff, the Islamic State group threatened to kill Haines next and briefly showed him on camera.
In the video posted Sunday, the group threatened to kill another British hostage. Both British men were dressed in orange jumpsuits against an arid Syrian landscape, similar to that seen in the Foley and Sotloff videos.
The SITE Intelligence Group, a U.S. terrorism watchdog, reported the video, which was also posted online by users associated with the Islamic State group.
The video was entitled "A Message to the Allies of America." Haines' purported killer, who appeared to be the same man speaking with a British accent as in the previous videos, tells the British government that its alliance with the U.S. will only "accelerate your destruction" and will drag the British people into "another bloody and unwinnable war".
Haines was abducted in Syria in 2013 while working for an international aid agency.
The British government had managed to keep his kidnapping secret out of concern for his safety until the most recent video identified him as a captive.
Late Friday, the family of Haines issued a public plea urging his captors to contact them.
In a short statement released through Britain's Foreign and Commonwealth Office, the family said: "We are asking those holding David to make contact with us."\
Watch: ISIS Beheads Briton David Haines, threatens to execute another Briton, Alan Henning