A U.S.-led coalition has been bombing ISIS targets in the Middle East for two years.

On Wednesday, the operation's commander said its bombs have killed 45,000 ISIS fighters in Iraq and Syria. Lieutenant General Sean McFarland estimated the terror group may be down to 15,000 fighters.

U.S. special operations forces are also on the ground in Syria, and for the first time we've seen video of them training soldiers to fight ISIS. But where the video came from is troubling.

Still from an ISIS propaganda video that claims to show U.S. special ops. CBS News

The ISIS propaganda video -- with English captions -- purports to show U.S.-backed Syrian rebels headed toward the ISIS stronghold of al-Bukamal, reports CBS News' Charlie D'Agata.

They're then stopped short by a hail of gunfire and forced to retreat.

The 20 minute video also appears to show American and British special forces with their New Syrian Army recruits at a training camp in Jordan.

One scene shows a blonde man described as an American coaching a Syrian fighter on how to speak in front of a camera.

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"Hand movements are no problem," he tells his trainee in Arabic, "but try not moving your legs."

ISIS could have seized the video off rebel fighters. A more worrying theory, says CBS National Security Analyst Fran Townsend, is that it could be the work of an insider.

"Has ISIS been able to penetrate Syrian rebel forces and get inside one of these training camps? That poses a whole host of security concerns, because you run the risk that once they have access to the training sites, it's a counterintelligence problem as well as a security problem," Townsend said.

The New Syrian Army has been America's latest hope in fighting ISIS on the ground -- specializing in counter-terrorism, and given the weapons and equipment to do it.

A still from an ISIS propaganda video claims to show U.S. weapons meant for rebel fighters in the hands of the terror group. CBS News

The video also alleges that some of those very weapons fell into the hands of ISIS after the rebel forces faced a crippling defeat last month. Thousands of rounds of ammunition, mortars, rocket-propelled grenade launchers, satellite phones, and even camera drones.

But the video itself may be just as damaging.

"It has to produce an internal investigation to understand how did this happen and why, and how can you prevent it. You certainly owe that to the security of the trainers and Syrian rebels who, by the way, won't want to have their identities revealed to ISIS," said Townsend.

We contacted U.S. military command in Baghdad and were told that they are aware of the video, but cannot comment on its authenticity. Furthermore, they cannot and will not discuss the ongoing missions of special operations forces.