A man stands by destroyed buildings after an airstrike by the Iraqi Air Force in Islamic State (IS) militants-seized city of Fallujah, some 50 kilometers west of Baghdad, Iraq, on Dec. 9, 2015. [Photo/Xinhua]

WASHINGTON -- The US-led coalition fighting the Islamic State (IS) has killed the extremist group's finance minister and two other senior leaders in airstrikes, the Pentagon said on Thursday.

IS finance minister Abu Salah, one of the most senior and experienced members of IS's financial network, was killed by US airstrikes in Iraq late November, said Steve Warren, spokesman for the US-led military campaign against the IS, also known as ISIL.

Warren said Salah was the third member of the finance network that had been killed in months.

"Killing him and his predecessors exhausts the knowledge and talent needed to coordinate funding within the organization," said Warren.

During the same timeframe, a senior leader of the group's extortion network and a third senior leader who acted as an executive officer had also been killed in airstrikes, Warren added.

Calling the IS the richest extremist group in history, US defense officials earlier this year estimated that the group had earned about $47 million each month from oil sales before October.