"Abu Sayyaf was killed during the course of the operation when he engaged US forces," a Carter's statement, published on Pentagon's website, said.
According to the statement, the secretary ordered to start the operation in eastern Syria on Friday's night. No US military personnel were killed or injured in the operation.
Carter pointed out that Sayyaf's wife Umm, who is suspected of also being involved in the terrorist activities, was captured by US forces.
The White House as well confirmed the results of the raid, adding that the US President Barack Obama authorized the operation upon the unanimous recommendation of his national security team.
According to National Security Council spokesperson Bernadette Meehan, Abu Sayyaf was a senior IS leader who, among other things, was overseeing militants' illicit oil and gas operations.
The White House stressed that the operation by the US Special Forces unit based out of Iraq was conducted with a prior consent of Iraqi authorities.
The Islamic State extremist group has seized vast territories across Syria and Iraq, gaining notoriety for its brutal methods, including mass executions.
A US-led coalition of some 60 nations has been carrying out airstrikes against the Islamic State targets in Iraq since August 2014, and in Syria since September 2014, albeit without the approval of the Syrian government.
