Sami Jasim Muhammad al-Jaburi, also known as Hajji Hamid, was a deputy of al-Baghdadi and a central figure in managing Daesh’s finances. Al-Jaburi was also a member of al-Qaeda in Iraq in the past.
The US Department of the Treasury designated al-Jaburi as a Specially Designated Global Terrorist in September 2015. An up to $5 million reward had been issued for any information concerning him.
Vote counting was underway in Iraq on Monday, a day after a record low turnout in a parliamentary election.
The turnout in Sunday's election was 41%, the electoral commission said. The lowest turnout was in Baghdad, with between 31% and 34%.
Election results are expected on Monday.