US forces have killed a senior Islamic State leader, among several key members of the militant group eliminated this week, the country's Defence Secretary Ash Carter said.

Mr Carter identified the senior IS leader as Haji Imam and described him as the group's finance minister. He said he was a "well-known terrorist" who had a hand in terror plots outside of Iraq and Syria.

"Leaders can be replaced. However, these leaders have been around for a long time. They are senior, they are experienced," Mr Carter told a Pentagon news conference.

Mr Carter did not say whether the IS finance leader was killed in Syria or Iraq.

Appearing at the news conference with Mr Carter, General Joseph Dunford, chairman of the Joint Chiefs of Staff, said there has been no fundamental shift in the US approach in Iraq, and he said efforts are under way to accelerate the campaign.

The US military has killed numerous Islamic State leaders in recent months. Earlier this month the Pentagon said it killed Omar al-Shishani, described as the Islamic State's "minister of war", in an air strike in Syria. In November, the Pentagon said an air strike in Libya killed Abu Nabil, another top IS leader.