British security officials are studying an Islamic State (IS) video that threatens more terrorist attacks against the United Kingdom.
Authorities were looking for clues about the identity of a masked man who speaks with a British accent in the video before shooting a man in the head for purportedly working as a British spy.
The man says IS extremists will soon invade Britain.
Four others accused of spying for Britain also are shot dead by other militants in the video who do not speak.
The video circulated on the Internet on January 3 features an apparent replacement for Mohammed Emwazi, the British-accented IS militant known as Jihadi John who was killed by a drone strike in Syria in November.
A spokeswoman for British Prime Minister David Cameron said on January 4 that the video "is clearly a propaganda tool and should be treated as such."