– American Special Operations forces mounted a rare raid into eastern Syria early Saturday, killing a senior leader of the Islamic State in Iraq and the Levant and about a dozen militant fighters, as well as capturing his wife and freeing an 18-year old Yazidi woman whom Pentagon officials said had been held as a slave.

In the first successful raids by U.S. ground troops since the military campaign against ISIL began last year, two dozen Delta Force ­commandos entered Syria aboard Black Hawk helicopters and V-22 Ospreys and killed Abu Sayyaf. A U.S. military official described him as the terrorist group's "emir of oil and gas."

Even so, Abu Sayyaf is a midlevel leader in the organization — one terror analyst compared him to Al Capone's accountant — and likely is replaceable in fairly short order. And the operation comes as ISIL has been advancing in the Iraqi city of Ramadi, demonstrating that the fight against the Sunni militant group in both Iraq and Syria remains very fluid.

Yet the Pentagon's description of a nighttime raid that found its intended target deep inside Syria without any American troops being wounded or killed illustrates not only the effectiveness of the Delta Force, but of improving U.S. intelligence on ­shadowy ISIL leaders.

A Defense Department official said ISIL fighters who defended their building and Abu Sayaff tried to use women and children as shields, but that the Delta Force commandos "used very precise fire" and "separated the women and children." The official said the operation involved "hand-to-hand fighting."

The U.S. forces eventually entered the building where they found Abu Sayyaf and his wife, Umm Sayyaf, in a room together.

His wife was captured and later moved to a military ­facility in Iraq.

The raid came after weeks of surveillance of Abu Sayyaf, using information gleaned from a growing network of informants the CIA and the Pentagon have developed in Syria, as well as satellite imagery, drone reconnaissance and electronic eavesdropping, U.S. officials said.

In a statement early Saturday, Defense Secretary Ashton Carter said the killing of Abu Sayyaf dealt a "significant blow" to the group. The terrorist leader was said to be involved in ISIL's military operations and helped direct its "illicit oil, gas and financial operations" that raised the funds necessary for the organization to operate. Officials said the raid was approved by President Obama.

Defense Department officials said the Delta Force soldiers carrying out the raid came under fire soon after they landed near a building used by Abu Sayyaf as his residence, in Al Amr, about 20 miles southeast of Deir al Zour, near the oil facilities that he oversaw.

The commandos had left Iraq aboard the aircraft, and were soon on the ground in Al Amr, a Defense Department official said.

They came under fire, the official said, and fired back, killing around a dozen ISIL fighters. "The objective was the building, a multistory building," the official said.

Abu Sayyaf "tried to engage" the commandos, the Defense Department official said, and was shot and killed. The commandos took his wife and the Yazidi woman back to the waiting American aircraft, which, by then, had sustained a number of bullet holes from the firefight with ISIL.

Defense Department officials said only ISIL fighters had been killed in the mission, and that they had received no reports of civilian casualties. But officials acknowledged they were still gathering information on the raid.

Officials said the U.S. forces were able to seize communications equipment and other materials from the site.

Saturday's raid into Syria represents an important threshold for the administration in showing that it will continue to send American ground troops into harm's way outside major war zones — as it has in Yemen, Somalia and Libya — to capture or kill suspected terrorists.

Although Abu Sayyaf was not a well-known figure, he was important as much for who and what he knew about ISIL's hierarchy and operations as for his actual job.

"He managed the oil infrastructure and financial generation details for ISIL," the senior U.S. official said on condition of anonymity. "Given that job, he was pretty well connected."