The attack on 6 May "targeted Abu Wahib, ISIL's military emir for Anbar province and a former member of al Qaeda in Iraq who has appeared in ISIL execution videos", the Pentagon press secretary Peter Cook said.

The strike was on a vehicle carrying Abu Wahib and three other Islamic State members near the town of Rutba, he said.

"We view him as a significant leader in ISIL leadership overall, not just in Anbar Province," Mr Cook added.

"Removing him from the battlefield will be a significant step forward."

Abu Wahib, also known as Shaqir Wahib al Fadhawi, is understood to have been the man in a 2013 video who quizzed truck drivers and executed three who failed to prove they were Sunni Muslims.

After the killings, Colonel Yassin Dwaij, head of Anbar province’s police intelligence, told the AFP news agency: "He is the only one who kills without covering his face, and is working on declaring an Islamic state.

"He is dangerous and cunning."

In May 2013, he was blamed for leading militants in kidnapping 16 policemen along the Iraq-Jordan highway in Anbar, leaving 12 of them dead and four injured.

The 30-year-old became a well-known figure with his thin black beard and monobrow and last year was ridiculed by members of Raqqa Is Being Slaughtered Silently, who said he looked like a doner kebab when wearing camouflage.

According to reports, he was drawn to terrorism while studying computer science at the University of Anbar.

He was arrested for links to al Qaeda in 2006 and held by US forces at Camp Bucca in southern Iraq until 2009, when he was sentenced to death and moved to a prison in Tikrit.

An al Qaeda-led riot at the prison allowed him and 109 other extremists to escape and return to their terror networks.