Inside the secret mission to rescue U.S. hostages in Syria; might future attempts be undertaken?

A U.S. Special Forces soldier searches a tree line for insurgent activity.(Photo: U.S. Department of Defense via ABC News)

WASHINGTON (WJLA/AP/ABC News) -- The White House this week disclosed that President Obama authorized a covert mission this summer to rescue American hostages in Syria, including journalist James Foley who was slain Tuesday by militants.

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Administration officials would not say specifically when or where the operation took place, citing the need to protect operational details in order to preserve the ability to carry out future rescue missions.

But a U.S. official with knowledge of the then-secret mission provided ABC News with new, dramatic details of the raid -- a mission that Secretary of Defense Chuck Hagel said was “flawless” except that no one was rescued.

A large contingent of American special operations forces was able to sneak into an ISIS camp near the terror group’s stronghold in Syria in search of American hostages, but quickly withdrew when it became clear that while 100 or so armed terrorists were there, the hostages weren't, according to the official.

“Knowing their lives were clearly in danger, it’s the responsibility of our leaders, our government to take action when we believe there is a good possibility or chance of making the operation successful. This operation, by the way, was a flawless operation, but the hostages were not there,” Secretary Chuck Hagel said. “We regret that mission did not succeed but I am very proud, very proud of the U.S. forces that participated in it.”

The White House said that nearly every branch of the military was involved and that the special forces on the ground were supported from the air by fixed wing, rotary and surveillance aircraft.

The U.S. official familiar with the operation said that the mission, at least from a military perspective, was “magic.”

When the “unusually large” U.S. special mission unit – described by senior officials as “several dozen” warfighters -- arrived at the location near Raqqah, Syria where they believed the hostages were being held, they had little time “on station” because of the distance they had to fly from their launch base.

A senior administration official said that “while on site it became apparent the hostages were not there.” But around 100 ISIS fighters were there, said the U.S. official familiar with the incident, and the American forces engaged in a fierce firefight. An Air Force AC-130 gunship came in overhead and put down fire on other ISIS fighters, keeping the bulk of the extremist force from the fight.

The Americans killed a number of ISIS fighters – at least 15, according to the U.S. official – before scrambling back to their helicopters and flying away.

The official said that some in the military and intelligence circles believe they missed the hostages by less than a week.

“It was magic,” the official told ABC News. “Everything went perfectly and [there were] no major injuries… But they saw it was a dry hole and left.”

Hagel declined to blame the incident on an intelligence failure.

“Was it a failure of intelligence? No. Intelligence doesn’t come wrapped in a package with a bow. It’s a mosaic of many pictures, of many factors, and the enemy always has a say,” Hagel said. “The underlying objective was to do everything we could to rescue these hostages, knowing that their lives were in danger, clearly in danger.”

Meantime, Foley's slaying has also reopened the debate over ransoms versus rescue attempts.

By rejecting demands for a nine-digit payment to save Foley, the U.S. upheld a policy choice that some European and Arab governments have long found too wrenching to make themselves: ruling out ransom to rescue any citizen held captive by militant organizations, in hopes the tough stand will make Americans safer from kidnapping and attacks by extremists.

Foley's beheading by the Islamic State extremist group has intensified a debate within the Obama administration and with American allies abroad about whether to pay ransoms to al-Qaida and other organizations, at the risk of encouraging more abductions and funding militancy.