A drone almost collided with a US commercial flight in March, an official with America's flight regulatory agency has revealed.
Jim Williams of the Federal Aviation Administration's (FAA) unmanned aircraft systems office said it showed the risks posed by such aircraft.
The near collision was reported to air traffic control as a pilot approached a Florida airport.
The FAA currently only allows non-commercial and police uses for drones.
But it requires drone pilots to alert an airport when flying it within five miles (8km) of the airport.'Catastrophic' results
"The airline pilot said that the UAS [unmanned aircraft system] was so close to his jet that he was sure he had collided with it," Mr Williams said at a drone conference in San Francisco.
"Thankfully, inspection of the airliner after landing found no damage."
American Airlines, which owns the aeroplane, said it was aware of the report and was investigating.
A FAA investigation was unable to identify the drone's owner or pilot, the agency said in a statement.
The use of drones has increased dramatically in the past few years as the aircraft have become cheaper and more accessible, putting the FAA under pressure to develop broader rules.
"Our challenge is to integrate unmanned aircraft into the busiest, most complex airspace in the world," the agency said in a statement.
"Introduction of unmanned aircraft into America's airspace must take place incrementally and with the interest of safety first."
Mr Williams said on Thursday the "risk for a small UAS to be ingested into a passenger airline engine is very real. The results could be catastrophic."