U.S. troops on the ground in Raqqa, Syria, are operating with fewer resources and have a limited ability to defend against the Islamic State drones. Here, a soldier aims an automatic rifle through a peephole in a wall Sunday in Raqqa. (Youssef Rabie/European Pressphoto Agency)

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.

The Pentagon, in response, is looking to send additional anti-drone equipment and troops into Syria, according to one official, who spoke on the condition of anonymity to discuss planning.

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.

In Raqqa, the Islamic State has been attacking U.S. targeting teams working alongside the coalition of Kurdish and Arab fighters, known as the Syrian Democratic Forces or SDF, the official said. The teams — usually operating from a vehicle with radios and a computer synced to communicate with the aircraft overhead — often have a spotter looking for incoming drones. In recent days, according to one SDF fighter, the Americans were preparing for a set of strikes after receiving coordinates from their Syrian counterparts when they had to move position because of a drone.

The Islamic State's use of drones is increasingly sophisticated, a worrying battlefield development with implications for other insurgencies. (Joby Warrick,Jason Aldag/The Washington Post)

“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.

It is unclear what type of anti-drone equipment and troops might be sent into Syria if the Pentagon decides to bolster its defenses there. 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.

U.S. troops often move around Mosul, deploying their vehicle-mounted Anti-Unmanned Aerial Vehicle Device, or AUDS, in locations that allow it to cover the Iraqi front lines. Other equipment to stop drones has also appeared in Iraq, including handheld rifles designed to disrupt the control signal sent to the aircraft. The counter-drone equipment, however, can come with a trade-off, as the gear has a tendency to scramble radios and other communication devices.

Placing counter-drone equipment around Raqqa could also be dangerous. In the last month, U.S. soldiers moving the devices around Mosul have come under fire from the Islamic State, at least once while scouting for deployment sites, according to troops familiar with the operations. Those troops also say that U.S.-led forces have committed resources to tracking and targeting Islamic State drone operators, sometimes using surveillance aircraft to track the drones back to their operators before striking.

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. Fighting in Raqqa has been heavy, but the U.S.-backed forces are making steady gains, especially in the eastern neighborhoods, officials said. Rocket artillery and Marine howitzers located on Raqqa’s periphery have also provided fire support for the advancing forces, especially during bad weather.