US commandos have mounted a rare raid into eastern Syria overnight, killing a senior Islamic State commander in a firefight, capturing his wife and rescuing a Yazidi woman held as a slave, the Pentagon said.
Defence Secretary Ash Carter announced the raid, identifying the militant as Abu Sayyaf. He said no US forces were killed or injured in the operation.
A US-led coalition has been striking Islamic State militants in Syria since last year but this is only the second time troops have carried out a ground raid. A previous operation was aimed at rescuing Americans held hostage by the group.
Syrian state media earlier reported that Syrian government forces killed at least 40 IS fighters, including a senior commander in charge of oil fields, in an attack on the country's largest oil field -- held by IS.
It identified the commander as Abu al-Teem al-Saudi. The name indicates he was a Saudi citizen.
It was not immediately clear why both Syria and the US would claim a similar operation in the Omar oil field. The US has said it is not cooperating with President Bashar Assad's government in the battle against the Islamic State group. But it has always said it gives the Syrian government a heads-up on operations within its borders.
The Britain-based Syria Observatory for Human Rights confirmed an oil field attack, saying at least 19 IS members, including 12 foreigners, were killed. The group did not say who carried out the attack.
A statement from the US National Security Council said Abu Sayyaf was a "senior ISIL leader who, among other things, had a senior role in overseeing ISIL's illicit oil and gas operations - a key source of revenue that enables the terrorist organisation to carry out their brutal tactics and oppress thousands of innocent civilians.
"He was also involved with the group's military operations."
It said President Barack Obama authorised the operation upon the "unanimous recommendation" of his national security team.
The statement also said the commandos rescued a young Yazidi woman "who appears to have been held as a slave" by the slain militant and his wife. IS militants captured hundreds of members of the Yazidi religious minority in northern Iraq during their rampage across the country last summer.
The extremist group controls much of northern and eastern Syria as well as northern and western Iraq. It has control of most of the oil fields in Syria, which are a key source of its funding. It has declared a caliphate in the territories under its control and governs them under a harsh version of Islamic law.