British intelligence services Monday were scrutinizing an Islamic State video released a day earlier in an attempt to determine the identity of a British-accented jihadist who threatened that the militant group would one day invade the U.K. and establish Islamic Shariah law there.

The BBC reported Monday that security services were working to compare the voice of the armed and masked man to those of individuals known to have traveled to Iraq and Syria.

Analysts for the British broadcaster suggested the video — which appeared to show the graphic execution of five men — might be an attempt to fill the shoes of the Islamic State fighter known as “Jihadi John,” the group’s English-language propagandist who appeared in prominent beheading videos.

The British accented jihadist threatened the Islamic State will invade the U.K. as he called the prime minister an "imbecile." (Screenshot: Islamic State video)

This masked British-accented jihadist threatened the Islamic State will invade the U.K. as he called the prime minister an “imbecile.” (Image source: Islamic State video)

Mohammed Emwazi, aka Jihadi John, was killed in a November drone strike in the militant group’s de facto capital of Raqqa, Syria.

The Guardian reported Monday:

British investigators do not yet know the identity of the man taunting [British Prime Minister David] Cameron and making threats directed against the UK. […]

To establish the identity of the man wearing the balaclava, British investigators will have to rely on voice analysis and by monitoring chatter on Twitter and other social media, as well as other electronic communication, to search for clues.

They might get lucky and establish his identity quickly, but the investigation is still at an early stage. It will probably be protracted — and is expected to take several months.

The video purported to show the point-blank shooting execution of five men accused of being spies for the U.K. and also featured a cameo appearance by a small boy dressed in military fatigues threatening “non-believers.”

The English-speaking and pistol-waving adult jihadist called British Prime Minister David Cameron an “imbecile” and a “slave of the White House” for trying to fight the Islamic State.

Comparing him to his predecessors Tony Blair and Gordon Brown, the Islamic State fighter said, “David, you are more of an imbecile” for daring “to wage war against a land where the law of Allah reigns supreme.”

“Only an imbecile would dare to anger a people who love death the way that you love your life,” the militant said.

He then threatened the U.K., where, based on his accent, it sounds as if he may have grown up.

“We will continue to wage jihad, break borders and one day invade your land where we will rule by the Shariah,” he said.

A little boy was also featured in the video threatening non-believers. (Image source: Islamic State group video)

A little boy is featured in a new Islamic State video threatening non-believers. (Image source: Islamic State group video)

According to the Guardian, the little boy in the video appeared to be around 7- or 8-years-old and said in English following the execution scene, “We are going to go kill the kafir [non-believers] over there.”

A Foreign Office source told the Independent that the video was “ISIS propaganda” meant “to divert attention away from its recent military failures in Iraq and its inability to look after the citizens in the areas it controls.”

The Associated Press reported that the 10-minute video — which TheBlaze is unable to independently authenticate — had the markings of the group’s media wing.

An estimated 800 British citizens have traveled to Iraq and Syria to fight for the Islamic State group.