Video shows beheading of British aid worker David Haines by ISIS

BEIRUT (KABC) -- A graphic video posted online Saturday shows the beheading of British aid worker David Haines by a self-professed member of ISIS.

The video emerged a day after the family of Haines issued a public plea Friday urging his captors to contact them.

Haines, 44, was abducted by militants in Syria 17 months ago. He had brought food and other supplies to Syrian refugee camps just across from the border with Turkey, when he was kidnapped.

Haines had appeared at the end of a video showing the beheading of U.S journalist Steven Sotloff on Sept. 2. At the end of the video, the group threatened to kill Haines.

In the video released Saturday, entitled "A Message to America's Allies", Haines is seen kneeling in an orange jumpsuit next to an armed masked militant dressed entirely in black. Haines gives a statement in which he says British Prime Minister David Cameron is "entirely responsible for (his) execution."

"You entered voluntarily into a coalition with the United States against the Islamic State (ISIS), just as your predecessor Tony Blair did, following a trend amongst British Prime Ministers who can't find the courage to say no to the Americans," Haines says.

The militant 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." At the end of the video, the militant threatened to kill a second British hostage.

Cameron condemned Haines' murder as "an act of pure evil" Saturday.

"My heart goes out to his family who have shown extraordinary courage and fortitude," Cameron tweeted. "We will do everything in our power to hunt down these murderers and ensure they face justice, however long it takes."

Cameron is expected to chair a meeting of the government's emergency response committee early Sunday.

Meantime, President Barack Obama strongly condemned "the barbaric murder."

"The United States stands shoulder to shoulder tonight with our close friend and ally in grief and resolve. We will work with the United Kingdom and a broad coalition of nations from the region and around the world to bring the perpetrators of this outrageous act to justice, and to degrade and destroy this threat to the people of our countries, the region and the world," Obama said.

Mike Haines said in a statement issued by the Foreign Office that his brother was devoted to humanitarian work.

"David was most alive and enthusiastic in his humanitarian roles," Mike Haines said. "His joy and anticipation for the work he went to do in Syria is for myself and family the most important element of this whole sad affair. He was and is loved by all his family and will be missed terribly."

Haines is the third captive to be killed by ISIS in such a public, brutal fashion. His murder follows the beheading of Sotloff and U.S. journalist James Foley.

Congressman Adam Schiff said the murder is staggering.

"First they execute journalists, now they're executing an AID worker, this is someone who devoted his life to helping people in need," Schiff said. "He was there helping refugees from this civil war and his reward from this group is to be beheaded."