An investigative report by a Bulgarian journalist says Saudi Arabia and the UAE have supplied Eastern European-made weapons to armed groups in Syria and Iraq using different intermediaries and diplomatic cover to mask their points of origin and final destinations.

The report, authored by Dilyana Gaytandzhiev, claims Saudi Arabia, UAE, the US military and several countries have used Azerbaijani state-owned airlines Silk Way Airlines to transport large quantities of weapons that ended up in the hands of the Islamic State of Iraq and the Levant (ISIL, known as ISIS) group, Kurdish fighters in the Middle East and armed groups in Africa.

"At least 350 diplomatic Silk Way Airlines flights transported weapons for war conflicts across the world over the last 3 years," says the report, published in Trud, Bulgaria's largest circulated newspaper.

"The state aircrafts of Azerbaijan carried on-board tens of tons of heavy weapons and ammunition headed to terrorists under the cover of diplomatic flights."

According to the report, "Saudi Arabia has purchased huge quantities of Eastern European weapons and exported them using Silk Way Airline's diplomatic flights.

"In 2016, 2017 there were 23 diplomatic flights carrying weapons from Bulgaria, Serbia and Azerbaijan to Jeddah and Riyadh".

Diplomatic flights

Gaytandzhiev says in the report: "The Kingdom [of Saudi Arabia] does not buy those weapons for itself, as the Saudi army uses only Western weapons and those weapons are not compatible with its military standard.

"Therefore, the weapons transported on diplomatic flights end up in the hands of terrorist militants in Syria and Yemen that Saudi Arabia officially admits supporting."

Citing leaked documents that detail flight paths and weapons cargo of the diplomatic flights, the report shows one aircraft loaded with mortars and anti-tank grenades including SPG-9 and GP-25 which were later discovered by the Iraqi army a month ago in an ISIL warehouse in Mosul.

Al Jazeera could not independently confirm the claims made in Gaytandzhiev's report.

The US news outlet Buzzfeed published an investigation in 2016 detailing how obscure and small American defence contractors were awarded big contracts by the US military to arm and equip Syrian opposition fighters using Eastern European weapons.

Saudi Arabia has publicly expressed its support for Syrian fighters trying to topple the Syrian government of President Bashar al-Assad.

Multiple attempts by Al Jazeera by phone and email to reach Silk Way Airlines in Baku for a reaction to the Trud story proved unsuccessful.

Gaytandzhiev said on Thursday in a tweet that she was fired from her job at Trud after she was interrogated by the Bulgarian national security which tried to find out her sources.

She said she first got suspicious of the weapons transferred to Syria when she found Bulgarian-made weapons at the hands "terrorists" in Aleppo while reporting on the Syrian war there.

She said that she then traced those weapons to its Bulgarian manufacturer only to find out that those weapons were legally exported to Saudi Arabia, which in turn supplied it to "terrorists" in Syria.

'Hands of terrorists'

Speaking to Al Jazeera by phone on Sunday from Bulgaria, Gaytandzhiev said: "Saudi Arabia, UAE and the US must stop using the cover of Silk Way Airlines diplomatic flights to supply Eastern European weapons which end up in the hands of terrorists around the world. Diplomatic flights are exempt from checks and inspection."

A joint investigation by Al Jazeera and the New York Times revealed a joint CIA-Saudi operation that supplied weapons to Syrian fighters by shipping through Jordan.

Many of the weapons, the investigation revealed, were stolen by Jordanian officers of the General Intelligence Department.

Some of the stolen weapons were used in a shooting in November of 2016 that killed two Americans and three others at a police training facility in Amman.

Historically, the United States has relied on Saudi Arabia to clandestinely finance weapons shipment to armed groups around the world from the Nicaraguan Sandinistas to Afghan Mujahideen in the 1970s and '80s to more recent and current Syrian and Iraqi fighters.