U.S. Special Operations forces killed a key ISIS commander

U.S. Special Operations forces killed a key ISIS commander during a daring raid in eastern Syria overnight Friday to Saturday -- securing intelligence on how the terror organization operates, communicates and earns money, U.S. government officials said.

The ISIS commander, Abu Sayyaf, was killed in a heavy firefight after he resisted capture in the raid at al-Omar, U.S. Secretary of Defense Ash Carter said in a statement.

Sayyaf's wife, an Iraqi named Umm Sayyaf, was caught and is being held in Iraq.

The ground operation was led by the Army's Delta Force, sources familiar with the mission told CNN. There were about two dozen members of Delta Force involved, sources said. They were part of a multi-branch force of about 100, the sources told CNN's Barbara Starr.

Carter said he had ordered the raid at the direction of President Barack Obama. All the U.S. troops involved returned safely.

National Security Council spokeswoman Bernadette Meehan said Obama had authorized the raid "upon the unanimous recommendation of his national security team" and as soon as the United States was confident all the pieces were in place for the operation to succeed.

"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 organization to carry out their brutal tactics and oppress thousands of innocent civilians," she said in a statement.

"He was also involved with the group's military operations."

Abu Sayyaf was a Tunisian citizen, a senior administration official said.

A U.S. official with direct knowledge of the intelligence and the ground operation described Sayyaf as "CFO of all of ISIS with expertise in oil and gas" who played a increasing role in operations, planning and communications.

"We now have reams of data on how ISIS operates, communicates and earns its money," the official told CNN, referring to some of the communications elements, such as computers, seized in the raid.

Umm Sayyaf, his wife, is currently in military detention in Iraq. A young woman from the Yazidi religious minority was rescued.

"We suspect that Umm Sayyaf is a member of ISIL, played an important role in ISIL's terrorist activities, and may have been complicit in the enslavement of the young woman rescued last night," said Meehan. ISIL is an alternative acronym for ISIS.

Meehan said Umm Sayyaf was being debriefed about ISIL operations, including any information she may have on hostages held by the terror group.

Abu Sayyaf and his wife are suspected to be involved in or have deep knowledge of ISIS hostage operations, a U.S. official with knowledge of the operation told CNN. A team from the FBI-led High Value Interrogation Group is expected to interrogate the wife, the source said. They will seek to figure out what she may know about the capture, movement and treatment of hostages.

But Michael Weiss, author of "ISIS: Inside the Army of Terror," said Abu Sayyaf was largely unknown to close observers of the organization.

Weiss said he's skeptical the United States would risk lives to capture the head of ISIS's oil operations. ISIS hasn't made significant money from captured oil fields since U.S. bombers began striking its infrastructure, he said.

A Pentagon spokesman confirmed in February that oil is no longer a main source of revenue for ISIS.

"It may be the case that he wasn't the primary target in this operation," Weiss said. "The U.S. might have been trying to kill or capture a higher-value ISIS leader who was thought to be at the same location. But it'd make sense to play up Abu Sayyaf's prominence after the fact since U.S. soldiers' lives were at risk here."

But risking American lives to capture Abu Sayyaf makes sense to Derek Harvey, a former U.S. Army colonel, intelligence officer and the director of the Global Initiative for Civil Society and Conflict at the University of South Florida.

"The most important thing about the raid is not getting Abu Sayyaf; it's getting his records," Harvey said.

Harvey asserted that Sayyaf was one of ISIS's top financiers, with likely access to the group's contacts with banks, donors, Turkish and Lebanese business interests as well as links to criminal and smuggling networks.

Sayyaf might not have been the intended target, Harvey acknowledged. But he had undeniable value as a target because ISIS is also a business.

"They're meticulous record-keepers," he said.

Meehan's statement added that Obama is "grateful to the brave U.S. personnel who carried out this complex mission as well as the Iraqi authorities for their support of the operation and for the use of their facilities, which contributed to its success."

Meehan said the U.S. did not coordinate with nor advise Syria in advance of the operation.

"We have warned the Assad regime not to interfere with our ongoing efforts against ISIL inside of Syria," she said, adding that the "brutal actions of the regime have aided and abetted the rise of ISIL and other extremists in Syria."