David Cameron has condemned a “disgusting and despicable” video apparently showing a second US journalist being beheaded by Islamic State militants.
The Prime Minister said: “It is an absolutely disgusting and despicable act.
“I will be making a statement later.”
The footage seemingly shows the same masked jihadi, believed to be British, who murdered James Foley last month.
The victim, named as American Steven Sotloff, is again pictured in an orange jump suit before the brutal act.
Mr Sotloff, who freelanced for Time and Foreign Policy magazines, was seized in Syria in August 2013 and had not been seen until he appeared in a video released online last month by the IS group.
In the video, Mr Sotloff reads out a purported personal “message to America” in which US president Barack Obama is told: “I am paying the price of your interference with my life.”
“You’ve spent billions of pounds US taxpayers’ dollars and we have lost thousands of our troops in our previous fighting against the Islamic State, so where is the people’s interest in reigniting this war?” the message adds.
The killer, believed to a British jihadist nicknamed “John” by captives, says: “I am back, Obama, and I am back because of your arrogant foreign policy towards the Islamic State, because of your insistence on continuing your bombings and … on Mosul Dam, despite our serious warnings.
“Just as your missiles continue to strike our people, our knife will continue to strike the necks of your people.”
The extremist also warns other governments against entering “this evil alliance of America against the Islamic State”.