New images released by the Islamic State show the recent shootdown of an Iraqi helicopter with a shoulder-fired missile, raising fresh concerns about the proliferation of such weaponry in the region and the limitations of American airpower.

The still images released by the Islamic State show the firing of a Chinese-made MANPADS system at a helicopter said to be over the city of Baiji in northern Iraq. The missile tracks upwards before hitting its target, what appears to be an Mi-35M gunship, causing the aircraft to catch fire before crashing.

Advanced systems like MANPADS, or man-portable air defense systems, present a particularly challenging threat for Iraqi forces. The U.S.-led bombing campaign in Iraq and Syria has been focused on conventional elements of the Islamic State’s military equipment, including tanks and artillery. MANPADS are highly portable and difficult to target.

“You’re not going to see a MANPADS until they fire,” said David Maxwell, associate director of the Center for Security Studies at Georgetown University. “It’s a very complex operation to suppress enemy air defenses, and I don’t know if the Iraqi army has the capability yet to conduct an integrated and combined fight of the likes it takes to defeat these kinds of capabilities.”

MANPADS are ideal weapons systems for “asymmetric” warfare, Maxwell said. Fighters can blend into populated areas and employ the systems only when they see targets of opportunity — like low-flying Iraqi helicopters.

As the Islamic State has marched across parts of Iraq and Syria, its fighters have overrun military facilities, collecting advanced weapons systems in the process. Arms researchers say they are seeing a greater array of MANPADS than they did before.

Matt Schroeder, a senior researcher with the arms research project Small Arms Survey, said the images released from the shootdown of the Iraqi helicopter in Baiji marked the first documented time the Islamic State is believed to have used the Chinese-made, heat-seeking FN-6 MANPADS in Iraq.

The FN-6 can hit targets flying at more than 11,000 feet. Other MANPADS, however, can reach much higher. The Russian-made SA-24, for instance, which has also been documented in the region, can hit targets flying at up to 20,000 feet.

Schroeder said he’s concerned about the Islamic State obtaining SA-24s. Late last month, the Iraqi Defense Ministry uploaded a video to YouTube showing Iraqi security forces receiving what appears to be a shipment of the advanced systems.

“I’m concerned that with the security situation as it on the ground that ISIS could seize the facilities that are storing those systems,” he said, using one of the acronyms for the Islamic State.

While difficult to identify the specific aircraft downed in Iraq recently, photographs of the wreckage show weapon systems consisted with the standard armament of the MI-35M, according to a report from IHS Janes. The Iraqi Defense Ministry confirmed that an Mi-35 was shot down near Baiji on Oct 3., as was a scout helicopter on Oct 8 in the same area.

The Mi-35 is billed to have advanced countermeasures to mitigate heat-seeking missiles. Those countermeasures, however, wouldn’t have been sufficient to protect the downed aircraft if the pilots didn’t take precautions.

“[The Iraqis] were probably flying the same route every day,” said a Marine pilot with experience flying over contested air space. The Islamic State fighters, he speculated, “figured it out and just waited for them, missiles and cameras in hand.”