Britain's Cameron 'horrified' by Kassig murder

 British Prime Minister David Cameron said on Sunday he was "horrified" after the Islamic State jihadist group claimed to have executed US aid worker Peter Kassig, known as Abdul-Rahman after converting to Islam, AFP reports.

"I'm horrified by the cold-blooded murder of Abdul-Rahman Kassig," Cameron wrote on Twitter. "ISIL have again shown their depravity. My thoughts are with his family."

The IS video, which is being examined by US intelligence officials and Britain's Foreign Office, also showed the gruesome simultaneous beheadings of at least 18 men described as Syrian military personnel, the latest in a series of mass executions carried out by IS militants.

Cameron called Kassig "a selfless humanitarian worker who had gone to the region to help" and said that the assumed killing "underlines the deplorable depths to which these terrorists are prepared to go".

The British government meanwhile has said it is looking into a newspaper report that "Jihadi John", a British-accented man who appeared in previous videos showing the killings of two US journalists and two British aid workers, had been injured in a US-led air strike last week.

Francis Dannatt, the former head of the British army, said the most recent beheading meant that Britain should consider joining air strikes on Syria as well as Iraq and Western leaders should keep the option of sending in ground troops open.

"Of course it means attacking ISIL from the air, it means attacking them from the air over Iraq and Syria -- and our government has got to think about that one very closely," he told Sky News, using the alternative name for the Islamic State group.

"If that is not enough then we might have to think the unthinkable and possibly engage Western forces on the ground," he said.

"We have got to keep all options open if we are serious about meeting that strategic objective of defeating and destroying Islamic State."