#usmexicoborder

The U.S. military’s border mission with Mexico is still ongoing, with thousands of troops deployed and no end date in sight.

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The unexpected and ultimately short-lived flight ban near El Paso this week stemmed from disagreements within the federal government over the use of a high-energy laser weapon system to take down drones, multiple sources told CBS News.

After training by the U.S. military, Customs and Border Protection used a palletized high-energy laser system earlier this week, even though the Federal Aviation Administration still has safety concerns, according to sources who were granted anonymity because they are not authorized to speak on the matter.

The system CBP used has been deployed overseas, according to two of the sources, but had not been considered for regular domestic use until recently. The system works by detecting an aerial threat, emitting a laser beam that can quickly zero in on the target, like a drone, and the beam's heat damages or disables the object.

High-energy lasers are one of several systems the government could use to counter drones.

"The laser, of course, is essentially instantaneous, and so it's relatively easy for something that's doing the speed of light to hit exactly the point on the object that it wants to do," said Tom Karako, a senior fellow and the director of the Missile Defense Project at the Center for International and Strategic Studies.

After Wednesday's flight restriction was lifted, Transportation Secretary Sean Duffy said "the threat has been neutralized" by the FAA and praised the Pentagon, which he said "acted swiftly to address a cartel incursion." But the Pentagon said it had nothing to add when asked when or how the threat was eliminated.

While CBP thought it was targeting foreign drones with the high-energy laser, it turned out to have taken down at least one party balloon, multiple sources told CBS News.