Pentagon spokesman Peter Cook said the May 6 strike near the town of Rutba -- deep in the Anbar desert -- targeted Abu Wahib IS's "military emir" for the vast western province.

Wahib was "a former member of Al-Qaeda in Iraq who has appeared in ISIL execution videos" Cook said using an acronym for the IS group.

"We view him as a significant leader in ISIL leadership overall not just in Anbar Province" he added. "Removing him from the battlefield will be a significant step forward."

The men were traveling in a vehicle when they were hit. Cook provided no additional details and did not specify if a warplane or a drone had carried out the strike.

The killing of Wahib is the latest in a series of attacks on senior IS leaders in Iraq and Syria where the jihadists still control huge tracts of land despite an intense US-led air campaign dating back to August 2014.

Some other recent targets include Suleiman Abd Shabib al-Jabouri an "ISIL war council member" Abd ar-Rahman Mustafa al-Qaduli -- the IS group's second-in-command also known as Haji Imam -- and Omar al-Shishani the man known as "Omar the Chechen" who was effectively IS's defense minister.

In February US special operations forces captured Sulayman Dawud al-Bakkar also known as Abu Dawud who was described as a chemical weapons expert.

"Since the start of 2015 we've targeted and killed more than 40 high-value ISIL and Al-Qaeda external attack plotters. We have removed cell leaders facilitators planners and recruiters" Baghdad-based military spokesman Colonel Steve Warren wrote online last week.

Despite many significant coalition gains against the IS group the jihadists still control the key cities of Raqa in Syria and Mosul in Iraq and assaults to recapture the towns are not expected for months.