Three engineers working in a Serbian weapons factory have been arrested on suspicion of spying for a "foreign organization," the country's interior ministry said on July 22.
The accused are all current or former employees at the state-owned Krusik factory which manufactures weapons and ammunition including 155 mm artillery shells.
Last month it was reported that Serbian-manufactured ammunition worth $855 million had made its way indirectly to Ukraine, despite Serbian-Ukrainian relationships complicated by Belgrade's friendly attitude toward Russia.
The three men are accused of "taking out confidential business-technical documentation from this company without authorisation and handing it over to a foreign organization," Serbian police said in a statement quoted by AFP.
It added that their actions were "to the detriment of security, defence, military and other interests, as well as weakening the power of the Republic of Serbia."
Several European countries have in recent months reported cases of espionage and sabotage suspected of being carried out on the behest of Russia.
Alleged Russian spy rings have been discovered in countries including Ukraine, the U.K., and Slovenia.
The U.K.'s domestic counter-intelligence and security agency Mi5 has reportedly been ordered to prioritize targeting spies over terrorists due to a significant recruitment drive by Russia, China, and Iran.
In May, it was revealed that Russia is recruiting violent right-wing extremists to carry out sabotage attacks in Europe and the U.K., raising concerns among intelligence chiefs.