The Pentagon says it is "reasonably certain" that a US drone strike in Syria has killed the Islamic State militant known as "Jihadi John".
Col Steve Warren said Thursday's attack in Raqqa had hit the intended target, but it would take time to "formally declare that we have had success".
Mohammed Emwazi, a Kuwaiti-born British militant, appeared in videos of the beheadings of Western hostages.
UK PM David Cameron said targeting Emwazi was "the right thing to do".
It is believed there was one other person in the vehicle targeted in the strike.
Col Warren said such "routine" attacks had killed on average "one mid- to upper-level IS leader every two days" since May.
However, the death of Emwazi would be a "significant blow" to IS, even though he had not been an "operational or major figure" for IS.