PRINCETON, NEW JERSEY – Venezuelan President Nicolas Maduro accused political foes of trying to kill him during an open-air speech Saturday using explosives-laden drones, prompting a host of questions about the alleged attack and who might have been behind it. Wherever the investigation leads, Maduro's allegations raised the specter of unmanned aerial vehicles being used by militant groups or others to launch bombing, chemical or biological attacks, a tactic that has long worried security experts. The market for commercial drones has flourished in recent years amid widespread availability and falling prices. So-called quadcopters -- drones with four rotors -- that can be operated from more than a mile away (1.6 km) and can fly for more than 20 minutes on one charge cost less than $1,000 to buy online, though they are generally capable of carrying only a limited payload. Militant groups such as Islamic State have used drones to carry out attacks by dropping grenades or crashing into infrastructure.

This is a very serious, looming threat that we are currently unprepared to confront,