British security officials are studying an Islamic State group video that threatens more action against the United Kingdom.

Officials are looking for clues Monday about the identity of a masked man who speaks with a British accent on the video before shooting a purported spy in the head. The man says the extremists will soon invade Britain.

Four others accused of spying for Britain are also shot dead by others who do not speak.

The video circulated Sunday features an apparent replacement for Mohammed Emwazi, the British-accented man known as "Jihadi John," who was killed in a drone strike in Syria in November. He had figured prominently in earlier IS propaganda videos.

It also features a young boy who threatens Britons at the end of the video.