Militant groups like Hezbollah and ISIS have learned how to weaponize surveillance drones and use them against each other, adding a new twist to Syria's civil war, a U.S. military official and others say.

A video belonging to an al-Qaeda offshoot, Jund al-Aqsa, purportedly shows a drone landing on Syrian military barracks. In another video , small explosives purportedly dropped by the Iran-backed Shia militant group Hezbollah target the Sunni militant group Jabhat Fatah al-Sham, formerly known as the Nusra Front.

A U.S. military official, who spoke anonymously because he wasn't authorized to discuss the matter publicly, said the U.S. military is aware of the development. Commanders have warned troops to take cover if they see what they might have once dismissed as a surveillance drone, he said.

The head of the Airwars project, which tracks the international air war in Iraq, Syria and Libya, said the weaponized drones are clumsy but will scare people.

"There are a million ways you can weaponize drones — fire rockets, strap things in and crash them," Chris Woods said. He added: "This is the stuff everyone has been terrified about for years, and now it's a reality."

The U.S. military official couldn't immediately authenticate the videos in question, adding that most of the incidents they are aware of involved weaponized drones that simply crash into their targets. But another former senior U.S. military official who viewed the videos said there was nothing to suggest they were fake.

'This is the stuff everyone has been terrified about for years, and now it's a reality." - Chris Wood, Airwars project

A number of militant groups in the Middle East, including ISIS, Jund al-Aqsa and Jabhat Fatah al-Sham, as well as Hezbollah and Hamas, have all released videos indicating that they have surveillance and reconnaissance drones. Syrian anti-government rebels and militias loyal to President Bashar al-Assad were also flying cheap quad- and hexacopters as early as 2014 to spy on each other.

The surveillance drones allowed those groups to collect data on enemy bases, battlefield positioning and weaponry and improve targeting.

In this April 11, 2014, picture, Free Syrian Army fighters fly a remote-controlled miniature aircraft with a camera attached — a device the fighters say is used to spy on forces loyal to Syrian President Bashar al-Assad. These drones can easily be weaponized and increasingly are, according to U.S. military members and an organization that tracks international air war. (Yaseen al-Bushy/Reuters)

ISIS launched a sophisticated propaganda video in 2014, "The Clanging of the Swords, Part 4," boasting about its capture of the Iraqi city of Fallujah. The video opens with drone footage over the western Iraqi city before cutting to violent ground footage depicting its advance across Iraq.

Lebanon-based Hezbollah has claimed to have armed-drone capabilities for nearly two years, but a recent video of bomblets hitting a militant camp near the Syrian town of Hama is the first known documentation.

Store-bought vs. military grade

The majority of these groups have access only to store-bought drones, similar to those available in the U.S., ranging in price from $1,000 to $3,000 and weighing between 5 to 10 pounds — certainly not enough to support a large bomb or rocket. Hezbollah is an exception, receiving most of its munitions — including its drones — from Iran.

"It's not going to change the overall balance of power in the region, but it matters by the very fact that these are things that are normally beyond the capability of insurgents or terrorists groups," said Peter Singer, author of the book Wired for War: The Robotics Revolution and Conflict in the 21st Century, and a senior fellow at the New America Foundation.

A U.S.-led coalition unmanned aerial vehicle flying over Kobani is pictured from Suruc in Sanliurfa province, on Oct. 13, 2014. Militant and rebel groups mostly have access only to store-bought drones — although Hezbollah receives military-grade drones from Iran. (Umit Bektas/Reuters)

Syrian skies are already bustling with traffic. Coalition forces have launched some 5,400 airstrikes on ISIS targets since September 2014. Drones account for only about seven per cent of America's total air operations in Iraq and Syria because the U.S. is "stretched really thin" with drone operations in Afghanistan, Yemen, Pakistan and elsewhere, Woods said.

Add a small amount of explosives to a small drone, and even the psychological factor is pretty significant. - SWim Zwijnenburg, PAX for Peace

Russia is also showing off its own drone capabilities — albeit somewhat primitive compared to the U.S. Last month, the Russian Defence Ministry launched a live online broadcast of drone footage of the besieged Syrian city of Aleppo to "provide transparency of ceasefire regime implementation."

There is no question the militant groups are outmatched in the sky. But as cells linked to ISIS pop up across Europe and the United States, the real concern is the potential impact these experimental small, flying bombs could have if launched over crowded cities.

"You already see things happening in Ukraine, gangs in Mexico are using drones, and in Ireland, gangs there are using surveillance," said Wim Zwijnenburg, a security and disarmament policy adviser at Netherlands-based PAX for Peace. "Add a small amount of explosives to a small drone, and even the psychological factor is pretty significant."