A teenager has posted a video online of a handgun rigged to a drone firing shots in a wood in Connecticut.
The Federal Aviation Administration has said it is investigating whether Austin Haughwout, 18, has broken its rules.
The FAA regulations prohibit the careless or reckless operation of a model aircraft.
Mr Haughwout’s father told a local news station that his son made the drone with help from a Central Connecticut State University professor.
A video posted to YouTube shows a four-propeller drone topped with a semi-automatic handgun, firing four shots in the woods.
The agency said it is working with police in Clinton, where Mr Haughwout lives.
Last year, the teenager made headlines when a woman was charged with assault after confronting him about flying a drone at a public beach.
Drone laws are being incrementally introduced in the US.
FAA rules say drones must be clear of surrounding obstacles, but do not specifically mention guns, though guidelines do advise civilians using drones that they could be fined for endangering people while using them.