London, Nov 13 (PTI): Notorious British Islamic State extremist Mohammed Emwazi, known as 'Jihadi John' after appearing in gruesome propaganda videos executing hostages, is believed to have been killed in US drone strike in Syria.

While the Pentagon is assessing whether the extremist was killed in the military action carried out in Syria, No 10 Downing Street has indicated that there is a "high degree of certainty" that he was killed in the attack.

Prime Minister David Cameron is expected to make a statement from Downing Street on the attack later today following reports from the US that the American military was 99 per cent certain that he had been killed in a drone strike.

Downing Street and UK Ministry of Defence sources were marginally less certain in their response to the reports of his death than US sources, but added there was a “high degree of certainty that he has been killed”.

A No 10 spokesperson added that the UK military had been working "hand in glove" with the US on the operation.

Announcing details of the strike overnight, Pentagon Press Secretary Peter Cook, said, "US forces conducted an airstrike in Raqqa, Syria, on November 12, 2015 targeting Mohamed Emwazi, also known as Jihadi John."

Emwazi participated in the videos showing the murders of US journalists Steven Sotloff and James Foley, US aid worker Abdul-Rahman Kassig, British aid workers David Haines and Alan Henning, Japanese journalist Kenji Goto, and a number of other hostages, the Pentagon said.

Emwazi, who speaks English and is believed to be born in Kuwait, is frequently seen in hooded hostage videos carrying out violent beheadings. The UK government was notified of the operation and notified families whose kin was executed by Emwazi.