Airports and other sensitive locations throughout the United States could be attacked by personal drones, the U.S. Department of Homeland Security warns. The agency's “intelligence assessment” doesn't mention of any specific threats in the U.S., though it comes after a number of recent incidents in which hobbyists' unmanned aerial vehicles (UAVs) have interfered with commercial airline flights.

The DHS report cites a number of international incidents in which terrorists and roving criminal organizations have deployed drones “to support illicit or violent activities.” Among them is an example where the Islamic State group -- also known as ISIS or ISIL -- used a UAV to record video footage that was used “to support an assault” on an Iraq oil refinery in 2014. The DHS report also states that failed terror attacks inside the U.S. in recent years also relied on drones.

“We cannot rule [out] the ability of future adversaries to acquire and use a commercially available [drone] as part of an attack within the Homeland,” said the warning, which widely circulated this week

In the past three years there have been 500 drone “encounters” at sites around the U.S., 218 of which have been related to aviation. Recently there were three drone sightings in as many days at John F. Kennedy International Airport in New York City, for instance, and the pilot of a personal aircraft needed to make a sudden swerve over southern New Jersey when he spotted a UAV about 1,000 feet in the air.

“While many of these encounters are not malicious in nature, they underscore potential security vulnerabilities that could be used by adversaries to leverage unmanned aerial systems as part of an attack,” the intelligence report states.