(Reuters) - Venezuelan President Nicolas Maduro accused political foes of trying to kill him during an open-air speech on Saturday using explosive-laden drones, prompting a host of questions about the alleged attack and who might have been behind it.

Venezuela's Interior and Justice Minister Nestor Reverol holds a placard with a picture of a drone during a news conference in Caracas, Venezuela August 5, 2018. Ministry of Interior and Justice/Handout via REUTERS

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 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.

There have also been incidents that raised the possibility of attacks on heads of state. In January 2015, a drone crashed onto the White House lawn after its operator lost control, prompting concerns that the U.S. president’s home could be vulnerable.

A few months later, a man protesting against Japan’s nuclear policy dropped a drone carrying radioactive sand from the Fukushima nuclear disaster onto the prime minister’s office, though the amount of radiation was minimal. Last month, Saudi Arabian security forces shot down a recreational drone near a royal palace, briefly prompting speculation of a coup attempt.

Some activist groups have also used drones to underscore their message. In July, the environmental justice group Greenpeace crashed a Superman-shaped drone into a French nuclear plant to demonstrate its vulnerability to attacks.

There is no known precedent of armed drones being used in Venezuela, though simple recreational drones have become common for photos and video production. They have become increasingly popular at opposition rallies to document the number of people present, which is frequently a subject of heated debate between supporters and adversaries of the government.

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Government regulations around the globe have struggled to keep up with the rapid proliferation of commercially available drones, according to Colin Clarke, an analyst with policy think tank the RAND Corporation.

“The facts on the ground far outpace law, policy and authority,” he said.

‘VERY SERIOUS, LOOMING THREAT’

In the United States, officials have warned that existing law does not adequately protect against possible crimes using unmanned aircraft systems, or UAS, including conventional attacks, cyberattacks, drug smuggling and surveillance.

“This is a very serious, looming threat that we are currently unprepared to confront,” two top officials with the U.S. Department of Homeland Security, David Glawe and Hayley Chang, wrote in testimony to Congress in June, seeking more power to track and disable drones. “Today we are unable to effectively counter malicious use of drones because we are hampered by federal laws enacted years before UAS technology was available for commercial and consumer use.”

But civil liberties advocates oppose granting the government broad authority to strike drones preemptively, citing potential overreach.

Many counter-drone systems, such as “jammers” intended to sever the link between an operator and a vehicle, may be difficult to deploy in non-combat zones because of the risk that they could interfere with crucial communications like commercial aircraft or law enforcement channels, according to Dan Gettinger, co-director of the Center for the Study of the Drone at Bard College (CSD).

“There are a number of challenges to deploying these measures in the domestic space,” Gettinger said. A report by the center recently identified more than 200 anti-drone systems on the market, aimed at either detection or interdiction.

The Federal Aviation Administration has adopted some rules governing drone use, including issuing licenses and restricting airspace. More than 100,000 remote pilot certificates have been granted by the FAA since new regulations went into effect in August 2016.

The U.S. Department of Defense sought $1 billion for counter-drone measures in its proposed 2019 budget, according to the CSD.

There are limits to the likely impact of any drone attack launched by non-state actors. In a recent post, Scott Stewart, an analyst with the global security consulting firm Stratfor, wrote that military ordnance or military-caliber drones are extremely difficult to obtain, while homemade explosives are typically far less lethal.

But experts say the psychological effects of a small but successful attack could far outstrip the actual physical damage, accomplishing the goal of spreading terror that many militant groups such as Islamic State and al Qaeda have made their mission.

“With a Twitter account and a toy drone, you can really cause a lot of panic these days,” Clarke said. “That’s a big part of terrorism – the psychological aspect. Even if you can’t kill large numbers of people, you can still cause fear.”