A new report detailing the proliferation of advanced anti-aircraft missiles among factions in Syria and a warning from the Federal Aviation Administration released Tuesday has once again highlighted the danger to commercial aircraft posed by the easily-transferable and highly lethal weapons currently in circulation throughout the globe.

The report, issued by Small Arms Survey a research agency that has monitored global arms trafficking since 1999, indicated that armed Syrian groups have acquired eight different models of Man Portable Air Defense Systems or ‘MANPADS’, three models of which have not been seen outside of government control until recently.

The newer generation systems in circulation are a cause for concern, the report says, noting that certain models like the SA-24, which were probably taken from government depots, can intercept aircraft flying at around 20,000 feet. The SA-7, one of the more prevalent MANPADS seen throughout the Syrian conflict, can only hit targets at around 4,000 feet.

On Monday, the FAA issued a Notice to Airmen (NOTAM) statement regarding the conflict in Syria, prohibiting U.S. pilots and airlines from flying in Syrian airspace. “There is a continuing significant potential threat to civil aviation,” the FAA said in a statement, which said that armed groups in Syria were in possession of anti-aircraft weapons that have the ability to threaten civilian aircraft.

The agency had previously warned pilots against flying in Syrian airspace but had not prohibited it altogether until now.