DENVER - Unmanned aerial vehicles -- or drones -- could be used in air strikes on American soil to counter an extraordinary threat like the 9/11 terrorist attacks, according to U.S. Attorney General Eric Holder. 

Holder's legal opinion was provided in response to an inquiry about armed drone use by U.S. Sen. Rand Paul, a  Kentucky Republican. 

Holder wrote the senator that it is possible a drone could be used in a domestic strike,  adding the scenario is "entirely hypothetical" and "unlikely to occur."

In February, 7NEWS traveled to Sierra Vista, Ariz., for an exclusive look at drones that patrol the U.S.-Mexico border. The small aircraft capture images from nearly 5 miles in the sky. 

While the drones flown by Customs and Border Protection do not carry weapons, other models of the aircraft can be equipped with missiles.

"This isn't the wild, wild west of aviation where it's shoot first, aim and ask questions later," said Steve Cowell, a member of a federal advisory committee on the use of unmanned aircraft in national airspace.

He stresses using a drone is no different than using a fighter jet to intercept a plane.
         
"There are protocols in place for a shoot-down. In order for that to take place, it has to go to the highest levels of our government," Cowell told 7NEWS.

In fact, Cowell said he believes the cameras and sensors onboard drones are so sophisticated they may lead to better decision-making during a crisis.

 "The pilots controlling these UAVs are going to have enhanced judgment as to whether we're looking at a friend or foe," he said.

While the United States government admits drones have been used to kill suspected terrorists who are American citizens overseas, the aircraft have not been used in a domestic air strike.