British Prime Minister David Cameron on Friday welcomed reports of the killing of "Jihadi John" in a US drone strike and called the attack an "act of self defence", the media reported.
Cameron stopped short of confirming the death of Mohammed Emwazi -- who he branded a "barbaric murderer" -- but said the targeted strike was "the right thing to do", a Daily Mail report said.
Pentagon officials say they are "99 percent" sure they have killed the world's most wanted man in the terror group's capital of Raqqa in Syria.
Cameron said Britain had been working "hand in glove" round the clock with its closest ally the US to track down and target the militant executioner, who was believed to be responsible for the deaths of several IS hostages, including Britons Alan Henning and David Haines.
He called it a "strike at the heart" of terror group IS.
In a statement outside 10 Downing Street, the prime minister said Emwazi remained a threat to innocent people, including those in Britain.
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"I have always said that we would do whatever was necessary, whatever it took, to track down Emwazi and stop him taking the lives of others.
"We have been working, with the US, literally around the clock to track him down," he said, adding: "This was a combined effort. And the contribution of both our countries was essential."
"Emwazi is a barbaric murderer. He was shown in those sickening videos of the beheadings of British aid workers.
"He posed an ongoing and serious threat to innocent civilians not only in Syria, but around the world, and in Britain too," Cameron added.
Earlier the Pentagon confirmed that US forces carried out an airstrike in Syria targeting Mohammed Emwazi. He came to be known as "Jihadi John" after appearing in several gruesome propaganda videos depicting the beheadings of eight hostages.
"Emwazi, a British citizen, participated in the videos showing the murders of US journalists Steven Sotloff and James Foley, American aid worker Abdul-Rahman (Peter) Kassig, British aid workers David Haines and Alan Henning, Japanese journalist Kenji Goto, and a number of other hostages," Pentagon press secretary Peter Cook said.
"We are assessing the results of tonight's operation and will provide additional information as and where appropriate."
Emwazi was born in Kuwait in 1988 and came to Britain in 1994 when he was six years old. His parents reported him missing in August 2013 and were reportedly told by police, four months later, that he was in Syria.
In August 2014, he made his first appearance -- with his face covered -- in the IS video showing the beheading of Foley.
His nickname "Jihadi John" was given to him by a group of hostages, who described him as part of an IS cell they named "The Beatles" because of their British accents. In February 2015, his identity was confirmed as Mohammed Emwazi.