Off-the-shelf drones armed with an improvised explosive device and radioactive material comprise an increasingly likely terrorist threat intelligence officials are keeping an eye on worldwide.

The weapon would be physically and sociologically "poisonous," Friedrich Grommes, a senior German intelligence official told McClatchy's Tim Johnson on the sidelines of the September 6-7 Intelligence and National Security Summit in Washington.

"Even if only a few people are affected," Grommes pointed out, a dirty bomb delivered from the air "serves completely the idea of terrorism."

Grommes is the international terrorism and international organized crime desk chief at Germany's Federal Intelligence Service (Bundesnachrichtendienst or simply the BND).

Public education may be one key to unlocking a counter-panic mechanism. "Depending on the situation," the US Nuclear Regulatory Commission reports, a radiological dispersal device (RDD) explosion "could create fear and panic, contaminate property, and require potentially costly cleanup. Making prompt, accurate information available to the public may prevent the panic sought by terrorists."

The technology "hasn't quite crossed the Atlantic," Chris Rousseau, director of the Integrated Terrorism Assessment Centre at the Canadian Security Intelligence Service, said at the summit. "It hasn't actually left the battlefield," Rousseau said, but "the question is at what point somebody's going to get the idea to use that here."

Drones will "increasingly" be relied on by non-state actors as a cheap and readily available weapons platform, Max Abrahms, counterterrorism theorist at the Council on Foreign Relations told Global Security in an email.

"It's just a matter of time before they're equipped with bombs and deployed against civilian targets in the West. UAV's have gotten so much cheaper that they'll increasingly be used by groups and individuals to sow destruction," Abrahms said.

ISIS has been eager to boast that its remotely piloted aircraft make up an "air force."

In Iraq this year, ISIS-controlled UAVs attacked a group of civilians with an IED, a lull period ensued as emergency crews and first responders arrived on the scene, then a suicide car bomber launched a follow up attack in coordination with the IED strike, Bridget Johnson, terrorism fellow at the Haym Salomon Center, reported after examining ISIS propaganda clips.