SEOUL — Seoul police are investigating how a South Korean man was allegedly able to run a weapons smuggling ring for 12 years and sell stolen U.S. military guns and ammunition out of a warehouse in central Seoul, a police spokesman said Thursday.

Police arrested the 30-year-old man, identified only by his last name, Moon, and two other men in January and accused them of illegally obtaining and smuggling military equipment believed to have come from U.S. military bases in South Korea. Police announced the arrests Thursday.

Police said they raided Moon’s warehouse in Seoul’s Dongdaemun district after getting a tip and conducting a long stakeout. They said they found about 1,000 weapons and pieces of ammunition, including M-16 rifle rounds, M-60 machine-gun barrels, bayonets, smoke shells, grenades, bulletproof helmets and vests, mine detectors, night-vision goggles and lenses, and parts needed to make firearms.

Much of the equipment was labeled “Property of U.S. Government.”

Seoul police and the U.S. military’s Criminal Investigation Command are still investigating where the weapons came from and how they were sold, the spokesman said.

U.S. Forces Korea spokeswoman Col. Jane Crichton said she had not received information about the arrests as of Friday afternoon.

Moon sold the equipment in person and on the Internet to ammunition collectors and “survival game” operators, Seoul police allege. Survival games, where participants are taken to remote areas and fight pretend wars, usually with plastic guns, are highly popular in South Korea among university students, online gamers and other groups. Businesses often pay for their employees to participate in the mock battles as a bonding experience.

The police spokesman, who spoke on condition of anonymity, said some of the weapons may have been used to commit crimes.

“[The] warehouse looked like an exhibition displaying all the military equipment,” he said.