A vehicle-mounted signals “jammer” provided to the Iraqi security forces by the U.S. have greatly reduced the ISIS drone threat in the battle for West Mosul, according to Iraqi generals.

What the Iraqis call the “interference machine,” or “parasite machine,” has been used effectively to counter the small, commercial drones that the Islamic State of Iraq and Syria had been deploying to drop hand grenades and other small explosives on advancing forces, the Iraqi generals told the Kurdish news agency Rudaw Tuesday.

“The Americans have brought in a very advanced machine to the right bank of Mosul,” or western Mosul, Maj. Gen. Najim al-Jabbouri Jabouri said, “It is like a big vehicle. ISIS can no longer send even one drone into the sky.”

Lt. Gen. Abdul Ghani al-Assadi, commander of the elite Iraqi Counter Terror Service units (CTS), said the drone issue “has been resolved completely. The CTS recorded 72 ISIS drone flights on the first day of the battle for West Mosul last month and “on the second day, we recorded 52 sorties,” al-Assadi said. “Then we used some machines, parasite machines. It became eight and five days before now, and until today, not even a single flight” as the CTS moved to recapture government buildings in West Mosul, he said.

#Mosul: #ISIS has captured armed drones from the #Iraq|i Federal Police in Western #Mosul. pic.twitter.com/c53Fb8aEyz — WorldOnAlert (@worldonalert) March 8, 2017

Air Force Col. John Dorrian, a spokesman for Combined Joint Task Force-Operation Inherent Resolve, would only describe the devices given to the Iraqis as “jammers.” Dorrian has previously said that U.S forces advising and training the Iraqis have their own jammers to counter drones.

An apparently different type of anti-drone weapon spotted in Iraq is DroneDefender, made by Battelle, which resembles an assault rifle but features a directed energy frequency jammer mounted on the frame. It has a range of about 400 yards and works by disrupting the links to the drone controller or GPS device.

Dorrian told Rudaw that “the Iraqi Security Forces are moving very rapidly right now. The enemy is not able to stop their advances. The only thing the enemy has still been effective in doing is using drones, and even this capability has been declining.”

The ISF backed by U.S. airstrikes began the operation to liberate Mosul in northwestern Iraq last Oct. 17. The eastern part of the city split by the Tigris River was retaken in late January and the battle for more densely populated West Mosul began on Feb. 19.