Prime Minister David Cameron this morning said an air strike may have taken out Mohamed Emwazi, better known as Jihadi John, in what he termed an "act of self defence".
The Prime Minister said the UK had been working with the US "around the clock to track him down" but "cannot yet be certain if the strike was successful".
The US airstrike was carried out in Raqqa, Syria, the self-appointed capital of the Islamic State in Iraq and the Levant (ISIL).
A US official told the BBC there was a "high degree of certainty" he was hit.
"He posed an ongoing and serious threat to innocent civilians not only in Syria, but around the world, and in the United Kingdom too," Cameron said. "He was ISIL’s lead executioner, and let us never forget that he killed many, many, Muslims too." He added:
He was intent on murdering many more people, so this was an act of self-defence. It was the right thing to do.
Emwazi was known for the brutal murders of Japanese citizens Kenji Goto and Haruna Yukawa, American journalists Steven Sotloff and James Foley and aid worker Abdul-Rahman Kassig, as well as British aid workers David Haines and Alan Henning.
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Cameron said "Nothing will bring back David and Alan. Their courage and selflessness stand in stark contrast to the empty callousness of their murderers. Their families and their friends should be proud of them, as we are. They were the best of British and they will be remembered long after the murderers of ISIL are forgotten."
Emwazi was born in Kuwait but grew up in London, graduating from the University of Westminster.