Islamic State militants stormed a Syrian airbase over the weekend, routing the remaining elements of the country’s army from northern Raqqah province and reportedly seizing a cache of shoulder-fired surface-to-air missiles.

The seizure of Tabqa air base, while not the first installation of its type to fall to militants, highlights the Islamic State’s gains in the region and the group’s continued pilfering of advanced military equipment, particularly the surface-to-air missile systems known as MANPADS, short for Man Portable Air Defense Systems.

Matt Schroeder, a senior researcher at the Switzerland-based research group Small Arms Survey and author of a recent report on MANPADS in Syria, believes that the takeover of Tabqa airbase could mark a “significant proliferation” of the weapons across the region.

“What we do know from previous airfield seizures is that these places are a source of MANPADS and similar weapons,” Schroeder said.

It is difficult to independently confirm that Islamic State seized MANPADS from Tabqa.  Charles Lister, an analyst at Brookings Doha Center who has tracked the flow of weapons in the region, tweeted a photo that purportedly showed an Islamic State fighter wielding what appeared to be MANPADS.

Schroeder did not know the model of the system but noted it has the characteristics of an SA-18 and other Soviet MANPADS.

“This is not a system we see often,” Schroeder said. “We know very little about it.”

The SA-18 is one of eight MANPADS variants in militant hands that have been documented by Small Arms Survey. While most are Soviet-era models, the Russian Federation SA-24 and Chinese FN-6 have been sighted in the almost four-year-old conflict.

For Damien Spleeters, an investigator for Conflict Armament Research who just 10 days ago was documenting the weapons of the Islamic State in northern Iraq and Syria, the takeover of Tabqa airbase is just another example of the Islamic State expanding its arsenal of advanced weaponry.

“Usually when you take an airbase you don’t just find one or two systems,” Spleeters said. “You find a lot more than that because airbases are meant to store those types of weapons.”

Spleeters added that the prevalence of advanced systems like the SA-24, which can hit aircraft flying at up to 20,000 feet, is “very worrying.”

Even so, both Spleeters and Schroeder stressed that MANPADS are “systems” made up of various components that have to be assembled before they can be used to shoot down an aircraft.

“There’s a limited shelf life for these type of weapons,” Spleeters said. “There’s a lot of parameters in the picture.”

Most MANPADS, for instance, depend on batteries, which usually lasts only a few years when in storage and a few seconds when activated. When powered, the battery allows the missile to lock on to its target, but only for “a brief window,” Spleeters explained. Once the battery is expended, the weapon is useless.

It’s possible militants are trying to work around that limitation by using a homemade recharging system for one particular MANPADS variant. C.J. Chivers, of the New York Times, first reported the case of a Syrian rebel with the SA-7 outfitted with such a system.

“If they have a recharging capability there’s no telling how many SA-7s might be available to them,” Spleeters said.

First fielded in the late 60’s, the SA-7 is one of the world’s most prevalent MANPADS. While a number of variants exist, it has been used to shoot down aircraft since the Vietnam War. State Department officials said they are concerned that the use of MANPADS poses a threat to civil aviation in Syria.

Rachel Stohl, an expert on arms control at the Stimson Center, believes that like prior conflicts in the region, that the Syrian civil war will have long standing ramifications for MANPADS proliferation in the Middle East.

“There’s no question that the region is going to have to deal with a legacy of these weapons,” Stohl said. “You don’t just put the immediate area at risk, there is a ripple effect.”

Stohl noted that the loss of Taqba airbase and its stores of weaponry highlights the need for aggressive stockpile management of MANPADS and the risks posed to the international community when a government loses control of its territory.

“These are government depots being raided,” Stohl said. “Hopefully this is an opportunity to have a dialogue about best practices when it comes to storing these types of weapons.”

“These instances rekindle an interest in bringing these systems under control,” Schroeder said. “When sent to volatile they regions have the ability to be pilfered en mass.”

U.S. officials say they have plans to address the proliferation of conventional weapons, like MANPADS, in Syria and are coordinating with partners in international organizations and non-profit groups.

This post has been updated to include comments from State Department officials.