Sixty-five Kalashnikov rifles, 37 Scorpion guns and 43 pistols were seized in the operation conducted by the police's counter-terrorism unit over the weekend, the ministry's anti-organised crime chief Ivaylo Spiridonov told a press conference.

Police also found eight kilogrammes (18 pounds) of highly explosive black powder, 14 rocket-propelled grenade launchers and tens of thousands of cartridges, he added.

The suspected ringleader of the weapons smuggling operation was held during the raids, along with six others.

Another 17 Kalashnikov rifles and 15 pistols equipped with silencers were also confiscated by police agents in the central town of Kazanlak, home to Bulgaria's biggest and oldest light arms and munitions maker Arsenal, where officials said the arms came from.

An operation producing fake identity documents was also uncovered in the Kazanlak raid.

The prosecution has ordered a full investigation to establish how the arms were smuggled out of the Arsenal plant.

"It was an inside job. The weapons were definitely taken out illegally from the plant," deputy chief prosecutor Ivan Geshev said.

After a slump following the collapse of communism in 1989, Bulgaria's arms industry has experienced a boom in recent years, fuelled by conflicts in the Middle East.

The country's arms exports reached 1.2 billion euros ($1.36 million) in 2017 with experts believing that many of the weapons sold to top buyers Saudi Arabia and the US have ended up in the hands of armed groups in Syria and Yemen backed by these countries.