World

UK's David Cameron calls emergency military, security meeting after British hostage beheaded

  • File-This Oct. 11, 2013, file photo shows British Prime Minister David Cameron speaking during an investment conference in Belfast, Northern Ireland. Islamic State extremists released a video showing the beheading of British aid worker David Haines, who was abducted in Syria last year, and Cameron late Saturday, Sept. 13, 2014, condemned his slaying as "an act of pure evil."  (AP Photo / Peter Morrison, File)

    File-This Oct. 11, 2013, file photo shows British Prime Minister David Cameron speaking during an investment conference in Belfast, Northern Ireland. Islamic State extremists released a video showing the beheading of British aid worker David Haines, who was abducted in Syria last year, and Cameron late Saturday, Sept. 13, 2014, condemned his slaying as "an act of pure evil." (AP Photo / Peter Morrison, File)  (The Associated Press)

  • File-This March 21, 2012, file photo shows Britain's Prime Minister David Cameron leaving 10 Downing Street in London, as he departs to the House of Commons. Islamic State extremists released a video showing the beheading of British aid worker David Haines, who was abducted in Syria last year, and Cameron late Saturday, Sept. 13, 2014, condemned his slaying as "an act of pure evil." (AP Photo/Matt Dunham, File)

    File-This March 21, 2012, file photo shows Britain's Prime Minister David Cameron leaving 10 Downing Street in London, as he departs to the House of Commons. Islamic State extremists released a video showing the beheading of British aid worker David Haines, who was abducted in Syria last year, and Cameron late Saturday, Sept. 13, 2014, condemned his slaying as "an act of pure evil." (AP Photo/Matt Dunham, File)  (The Associated Press)

  • File-This Aug. 28, 2014, file photo shows President Barack Obama speaking about the economy, Iraq, and Ukraine, in the James Brady Press Briefing Room of the White House in Washington.  Obama on Saturday, Sept. 13, 2014, condemned as a "barbaric murder" the slaying of British aid worker David Haines by Islamic State extremists. Haines was abducted last year in Syria, and extremists released a video on Saturday showing his beheading. In a statement issued Saturday night, Obama said the hearts of Americans go out to Haines' family and the people of the United Kingdom. (AP Photo/Evan Vucci, File)

    File-This Aug. 28, 2014, file photo shows President Barack Obama speaking about the economy, Iraq, and Ukraine, in the James Brady Press Briefing Room of the White House in Washington. Obama on Saturday, Sept. 13, 2014, condemned as a "barbaric murder" the slaying of British aid worker David Haines by Islamic State extremists. Haines was abducted last year in Syria, and extremists released a video on Saturday showing his beheading. In a statement issued Saturday night, Obama said the hearts of Americans go out to Haines' family and the people of the United Kingdom. (AP Photo/Evan Vucci, File)  (The Associated Press)

Prime Minister David Cameron is summoning military and security chiefs for an emergency meeting in response to the beheading of a British hostage and a threat against another.

The Sunday meeting comes after Islamic extremists released a video showing the beheading of British aid worker David Haines and threatening another with death.

Haines is the third Westerner beheaded in recent weeks by the Islamic State group, which has seized vast swaths of territory in Syria and Iraq.

The 44-year-aid worker's family had issued a plea to his captors the day before the video was released urging the hostage-takers to contact them.

Haines was kidnapped in Syria last year.

His family has released a statement praising his charitable work and saying he was most alive when helping others.