Over the past several months, ISIS has released a number of propaganda videos sensationalizing their autonomous attack capabilities. Here is just one example of such propaganda.

#Mosul: Video shows #ISIS SVBIED attack in Western #Mosul. Army tried to stop it, but missed the SVBIED 2 times. pic.twitter.com/Ite5tYveFg — DroneAssad (@DroneAssad) June 10, 2017

In reality, the Pentagon has confirmed that the Islamic State's real drone program consists primarily of rather unsophisticated, off-the-shelf drones that have been retrofitted to drop 40mm grenade-sized munitions. That said, as the Washington Post points out today, despite their lack of technological sophistication, the ISIS drone program is becoming far more of a threat to U.S. troops serving in Raqqa and often operate in "swarms" to drop numerous grenades on troop positions simultaneously.

Islamic State drones are attacking U.S. Special Operations forces located around the group’s de-facto capital of Raqqa in Syria, U.S. officials and Syrian fighters said, sometimes disrupting the ability of American troops to call in airstrikes. Unlike in Mosul, where U.S. forces have deployed an array of drone-stopping systems, U.S. troops on the ground in Raqqa are operating with fewer resources and have a limited ability to defend against the small, hard-to-spot aircraft, the official said. The off-the-shelf drones, sometimes used in swarms by the extremist group, are often rigged to drop small 40mm grenade-sized munitions with a relatively high degree of accuracy.

While there have been no U.S. causalities reported in Raqqa from the ISIS drone program, it has impeded SDF advances.

“There have been no casualties, yet,” the official said. The attacks, according to the fighter, who spoke on the condition of anonymity because he wasn’t authorized to talk to the media, have also hindered SDF advances. He said that the Islamic State will wait for the SDF to send up its own drone before deploying an aircraft loaded with explosives so that those on the ground think a friendly drone is overhead.

As the Post notes, the Pentagon, in response to the growing threat, is considering whether to send additional anti-drone equipment and troops into Syria though it's currently unknown what that might entail.

Around Mosul, soldiers from the U.S. Army’s 82nd Airborne Division have steadily increased counter-drone operations since March, at a time when the Islamic State was becoming increasingly lethal with the devices.

The drone attacks around Raqqa come as U.S. Special Operations forces contend with larger unmanned aerial threats in southern Syria. Last week, an Iranian Shahed-129 — a drone roughly the size of a U.S. Predator — attacked U.S.-led Special Operations forces near the border outpost of al-Tanf, according to an intelligence official who spoke on the condition of anonymity to discuss the aircraft type. The munition launched by the drone appeared to be a dud and did not cause any casualties. The drone was subsequently shot down by a U.S. Air Force F-15E strike aircraft.

While the exact number of U.S. forces in Syria is unknown, there are at least several hundred U.S. Special Operations troops — a mixture of Green Berets, Rangers and other units — operating alongside the SDF as they push into Raqqa, while dozens are located around Tanf to the south.