Internet video purports to show Islamic State group beheading British hostage Alan Henning.

This undated family handout photo shows British man Alan Henning, who was held hostage by the Islamic State group. An Internet video released Friday purports to show an Islamic State group fighter beheading British hostage Alan Henning and threatening yet another American captive, the fourth such killing carried out by the extremist group now targeted in U.S.-led airstrikes. The video mirrored other beheading videos shot by the Islamic State group, which now holds territory along the border of Syria and Iraq. It ended with an Islamic State fighter threatening a man they identified as an American. (AP Photo/PA Wire) UNITED KINGDOM OUT NO SALES NO ARCHIVES (The Associated Press)

This undated photo provided by Kassig Family shows Peter Kassig standing in front of a truck filled with supplies for Syrian refugees. (AP/Kassig Family)