The operation followed an investigation led by the province's cybercrime police, who uncovered the network through online monitoring.
On June 5, investigators deployed five teams to northern provinces, including Thai Nguyen and Bac Giang, to identify and question suspects.
Searches uncovered more than one tonne of components and materials, including triggers, firing hammers, barrels, suppressors, steel pellets, air valves, bullet moulds, lead wire and other parts used to assemble PCP air rifles and military-grade weapons.
Police also questioned 151 suspected buyers and seized 57 firearms, more than 2,000 lead pellets, compressed-air cylinders, high-pressure pumps, metalworking equipment and a large quantity of gun-making tools and components.
Investigators said the suspects used social media, e-commerce platforms and courier services to sell gun parts, using unregistered phone numbers and disguised shipments to evade detection.
Based on the evidence collected, investigators opened a criminal case on June 7 over the illegal manufacture and trafficking of military-grade weapons.
Police charged three suspects, including Dao Huy Duc, 28, and Dao Thi Lan Anh, 21, both from Bac Ninh Province, with illegally possessing and trafficking military-grade weapons. Lai Van Hung, 34, from Thai Nguyen Province, was charged with manufacturing, possessing and trafficking the weapons.
Police said investigations were continuing to identify other people involved in the network.
