The Pentagon said on Friday it was "reasonably certain" a US drone strike had killed "Jihadi John", an Islamic State (IS) militant widely known for participating in the beheadings of Western hostages in IS's videos.

Calling the IS militant Mohamed Emwazi "a recruitment tool for the organisation", Pentagon spokesman Steve Warren told reporters at a briefing that the Pentagon was "reasonably certain that we killed Jihadi John", Xinhua reported.

However, the confirmation would still take some time, he added.

The US military launched a drone strike on Thursday targeting Emwazi around the Syrian city of Raqqa, headquarters of the IS in Syria, said a Pentagon statement released Thursday night.

Hailing from an affluent family in West London, Emwazi, a Briton born in Kuwait, reportedly travelled to Syria around 2012 to joined the IS during the group's infancy.

He gained the moniker of "Jihadi John" after appearing in a video about the beheading of American journalist James Foley last August.

He has also appeared in other videos documenting the appalling beheadings of other IS hostages, some of whom he had personally executed.