A Bulgarian reporter has uncovered evidence that the United States and its allies, notably Saudi Arabia and the United Arab Emirates, have been using Azerbaijan’s Silk War Airlines to ferry entire planeloads of weapons to Syrian militants, some of which ended up in the hands of al-Qaeda’s Nusra Front.

Some 350 different flights, all labeled “diplomatic” flights to avoid being searched for weapons, were sent into the area, generally carrying arms purchased in Eastern Europe, so as to disguise the country that was actually sending them.

This was the mechanism through which the since ended CIA program to arm Syrian rebels was conducted, and they apparently encouraged both Saudis and the Emirates to use the same trick. Exact figures on weapons sent aren’t total clear, but the US sent around $1 billion worth of arms by themselves.

The US apparently favored this program so much that they didn’t confine it to Syria, with the report showing cargo planes under the same diplomatic auspices being sent to Iraq, Pakistan, and Afghanistan. Exactly who was to be armed in those countries wasn’t clear.

It is clear, however, that this wouldn’t have been the method through which the US nor any other nation would legitimately convey arms deals or even military aid to other governments, and was specifically chosen because, despite the added cost, it was hoped that it would allow the shipments and deliveries to happen in secret.

Silk Road Airlines also apparently favored this scheme themselves, having “offered diplomatic flights to private companies and arms manufacturers from the US, Balkans, and Israel, as well as to the militaries of Saudi Arabia, UAE, and US Special Operations Command (USSOCOM), and the military forces of Germany and Denmark in Afghanistan and of Sweden in Iraq.”

Azerbaijan’s government was apparently well aware of this, and their foreign ministry was sending orders to their embassies across the region to ensure that the planes were given diplomatic clearance to fly “dangerous” materials through foreign airspace without a permit.

And it worked. Despite legal restrictions on carrying military cargo on civilian aircraft, the Azeri government managed to get diplomatic clearance for these planes that gave them an effective corridor across Europe and including Turkey. This gave the planes access to arms markets in Eastern Europe and arms-hungry wars in the Middle East and beyond.

While the revelations in Syria are likely old news, since the CIA’s failed arms program was already scrapped, it’s not clear that this isn’t still an ongoing means of arms smuggling for the US or its allies elsewhere. The revelation could be particularly embarrassing in Afghanistan, as there aren’t third parties to arm there who aren’t explicitly enemies of the US.

In buying non-US standard weapons, even when these arms ended up in the wrong hands, which at times may well have been the intended hands in the first place, there was some distance between the arms and the nations providing them. With most of Eastern Europe still selling Soviet-era surplus, this may well explain, for instance, why the Taliban has suddenly been seen with at least some such arms, with US officials trying to shift suspicion about that to Russia.

Clearly, though, there’s no way to prove the US sent those specific arms to the country and that’s the point. These smuggled arms stand in stark contrast to the massive, and at least nominally documented, official arms shipments the US is sending across the world at all times, and are meant to fly under the radar.