The United States did not warn the Syrian government in advance of a US special forces raid that killed a senior Islamic State leader in Syria, the White House said.
American special operations forces killed Abu Sayyaf, who directed the group's oil, gas and financial operations, in a raid in eastern Syria on Saturday.
The White House said President Barack Obama ordered the overnight attack, adding that ISIS commander's wife, Umm Sayyaf, was captured in the raid and was being held in Iraq.
She is believed to have played an important role in ISIS's terrorist activities. At least 16 ISIS fighters were killed in the raid.
During the operation, US forces said they had freed a young Yezidi woman "who appears to have been held as a slave by the couple."
This is the first known US special forces operation inside Syria aside from a failed secret effort to rescue a number of hostages held by Islamic State in northeastern Syria last year.
White House National Security Council spokeswoman Bernadette Meehan said in a statement that US personnel based out of Iraq conducted the operation in al-Amr in eastern Syria.
"During the course of the operation, Abu Sayyaf was killed when he engaged US forces," Ms Meehan said.
"The president authorised this operation upon the unanimous recommendation of his national security team and as soon as we had developed sufficient intelligence and were confident the mission could be carried out successfully and consistent with the requirements for undertaking such operations," Ms Meehan said.
Adding the operation was conducted "with the full consent of Iraqi authorities" and "consistent with domestic and international law."
The White House said the US did not inform Syrian President Bashar al-Assad's government in advance of the raid, or coordinate with Damascus.
"The U.S. government did not coordinate with the Syrian regime, nor did we advise them in advance of this operation," said Ms Meehan.
"We have warned the Assad regime not to interfere with our ongoing efforts against ISIL inside of Syria," she said, using an alternative acronym for Islamic State.
"The Assad regime is not and cannot be a partner in the fight against ISIL."
Shortly before the US announcement, Syrian state television said the Syrian army killed an Islamic State leader responsible for oil-related affairs, identifying him as Abu al-Taym al-Saudi.