The smuggled dual-use goods included optical sights, binoculars, aeronautical radio communication systems, ballistic calculators and software, regional prosecutor Vania Hristeva told a press conference.

The military equipment was purchased in Europe since early 2021, repackaged in Bulgaria and then smuggled into Russia via a commercial company based in the country's southern city of Plovdiv, police said.

The goods "were intended for Russian units involved in the war in Ukraine", such as the paramilitary group Wagner, according to the head of the national security agency, Plamen Tonchev.

Authorities said they have arrested twelve people in total, including three Russians, a Belarussian and an Albanian.

Five of them have been charged with "participation in an organised criminal group" and "illegal exports", offences punishable by prison sentences of up to 10 years.

The network was allegedly also operating in the United Kingdom, Switzerland, Serbia, Singapore and the United Arab Emirates, police said.

Authorities had investigated the case in cooperation with foreign services.

Even before Russia's invasion of Ukraine in February 2022, the European Union imposed sanctions on Russia following its annexation of Crimea in 2014.

Among the 2014 sanctions is a ban on exporting "dual-use goods and technology" that can be used for both military and civilian purposes.

A member of the European Union and NATO, Bulgaria is a Slavic and Orthodox country with close historical and cultural ties to Russia.

But relations have been strained since Russia launched its war against Ukraine.