Delta Force Commandos Kill Key ISIS Leader in Ground Raid in Syria

— -- In a ground raid deep in Syrian territory, U.S. special operations forces killed a top ISIS leader who they were attempting to capture and interrogate about American hostages and how the terror group finances its war machine, the Obama administration said today.

Officials told ABC News that the large-scale operation that killed ISIS oil and gas "minister" Abu Sayyaf was carried out by the Army's elite counter-terror unit known as Delta Force under the direction of the Joint Special Operations Command (JSOC).

Sayyaf was a Tunisian who the U.S. wished to question about the terror group's financing and about hostages murdered by ISIS including Kayla Mueller of Prescott, Arizona, the last known American captive. Mueller's death was announced by ISIS in February and confirmed by the White House.

One knowledgeable counter-terrorism official told ABC News that it was strongly suspected since last year that Sayyaf was the ISIS leader who ABC News previously reported had been given Mueller as a forced bride or slave. On Saturday, spokespersons for law enforcement and at the White House would not comment on such "speculation."

The Mueller family had no immediate comment either, according to their spokesperson, who added that they are monitoring the situation as it develops.

A concept of operations to capture Sayyaf was approved by President Obama in early March shortly after Mueller's death was announced, two counter-terrorism officials told ABC News. The NSC declined to comment on the timeline of Obama's approvals.

Mueller, a young aid worker, was the fourth American killed in ISIS hands and the last of those known to be held, therefore mounting an operation on the ground no longer jeopardized any hostages' safety, officials noted.

The raid was conducted overnight by a team of American Delta Force commandos who flew from Iraq into "eastern Syria" aboard V-22 Osprey aircraft and Blackhawk helicopters.

One senior U.S. official said there was "a pretty good fight on the ground." The adversaries used women and children as human shields but no innocents were killed. The battle got so close and intense that there was even some hand-to-hand combat, according to the official.

By the time the operation was over many of the aircraft were riddled with bullet holes, the U.S. official said. The entire operation lasted several hours from the time Delta Force operators took off from inside Iraq and eventually returned with no injuries or loss of life.

JSOC had been tracking Sayyaf since last year given his importance to ISIS, the two counter-terrorism officials told ABC News. The mission was set to launch by mid-March but weather and other conditions delayed it. Some officials had anticipated that Sayyaf would eventually be brought to New York to face terrorism charges, had he been captured alive.

"The President authorized 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," a White House National Security Council statement said Saturday morning.

The operation was coordinated with Iraq officials, but “the U.S. government did not coordinate with the Syrian regime, nor did we advise them in advance of this operation,” NSC spokesperson Bernadette Meehan said.

The American commandos took Abu Sayyaf's wife Umm Sayyaf into custody and rescued a female Yazidi captive "who appears to have been held as a slave by the couple," according to the NSC.

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 organization to carry out their brutal tactics and oppress thousands of innocent civilians," the NSC statement said. "He was also involved with the group's military operations."

The Sayyafs were also believed to have direct knowledge of American and other western hostages killed while in ISIS captivity. American families of the four who had been killed by the terror group in Syria were contacted by the Obama administration in the hours before the operation was launched by Delta Force, U.S. officials and other sources told ABC News.

“We are currently debriefing the detainee [Umm Sayyaf, held by the U.S. in Iraq] to obtain intelligence about ISIL operations. We are also working to determine any information she may have regarding hostages – including American citizens who were held by ISIL," Meehan said. "We have been in touch with the families of those American hostages previously held by ISIL, and the governments of nations with citizens held captive by ISIL. Given the sensitivity of those discussions, and out of respect for these families, I am not going to provide any additional detail about what was discussed."

On July 3, 2014 an entire squadron of Delta operators raided an old oil refinery site south of Raqqa, Syria, where Americans James Foley, Steven Sotloff, Peter Kassig and Kayla Mueller had been detained with other western hostages. At the time the hostages were alive, but they had already been moved and the commandos missed them by one or two days, President Obama later said.

Killing the ISIS oil "minister" Sayyaf is a major success because of his important role in selling the oil in Iraq and Syria that bankrolls the terrorist group's operations, officials said.