U.S. airstrike against "Jihadi John" was "act of self-defense": British PM

British Prime Minister David Cameron on Friday said Britain and the United States had been working "around the clock" to track the Islamic State (IS) group militant Jihadi John and that the U.S. drone strike against him was "an act of self-defense."

Speaking outside 10 Downing Street Friday, Cameron described Mohammed Emwazi, a masked IS fighter known as Jihadi John pictured in videos showing beheadings of western hostages, as an "ongoing and serious threat" to civilians around the world.

The U.S. military launched a drone strike on Thursday targeting Jihadi John, the infamous black-clad Kuwaiti-born Briton from west London. He was believed to be the chief executioner of western hostages kidnapped by IS, also known as ISIL or ISIS.

The airstrike was launched around the Syrian city of Raqqa, headquarters of the IS in Syria, and the United States is assessing the results of the operation, said Pentagon spokesman Peter Cook in a statement.

Cameron said any successful attack would have been "a strike at the heart of ISIL," and the strike against him was "the right thing to do."

"It will demonstrate to those that would do Britain, our people and allies harm, we have a long reach, we have unwavering determination and we never forget about our citizens," the prime minister said.

"He was ISIL's lead executioner and let us not forget he killed many, many Muslims too, and he was intent on murdering many more people," he added.

Emwazi, who speaks with a British accent, has long been suspected of being from Britain since he appeared in IS videos last year. Endit