The raids, which took place in May, were reported by the Pyeongtaek police department in a news release on Wednesday.
Police said they carried out search and seizure operations at Camp Humphreys, south of Seoul – the largest US military installation outside of the United States – and Camp Casey north of the capital, after receiving intelligence from the US Army Criminal Investigation Division.
Police videos of the raids show officers entering residential buildings and putting handcuffs on several individuals, both men and women.
Two people – a South Korean and a Filipino – were arrested for alleged drug distribution. After being taken into custody, they were transferred to the prosecution for indictment, police told CNN.
Another 20 people, including 17 US soldiers, were brought in for questioning but not detained, and sent to the prosecution for further investigation, police said.
CNN has reached out to the United States Forces Korea for comment.
Recreational use of cannabis is illegal in South Korea, where drugs are a social and cultural taboo and users face harsh penalties. The maximum sentence for cannabis use or possession in the country is five years in prison or a fine of up to 50 million Korean won (about $37,600).
The police news release alleged that between May and August this year, a 24-year-old American soldier had smuggled 350 milliliters [11.8 oz] of liquid synthetic cannabis sent from the US mainland via military mail, then distributed and sold it to other US soldiers based at Camp Humphries and Camp Casey.
The soldier, who is among those questioned, sold the drug to a Filipino distributor, who then sold it to a South Korean distributor and other US soldiers, the release alleged.
During the raid, police seized 80 milliliters of synthetic cannabis, 27 electronic cigarette devices and nearly $13,000 in cash allegedly earned from drug sales, the release said.
Videos released by the police show the seized items, with rolls of $50 and $100 bills, as well as numerous cell phones and colorful cylindrical tubes that look similar to vape pens.
The release added that police are cooperating with the US Army Criminal Investigation Division to investigate the US soldiers, as well as the alleged drug sender in the US and the smuggling route.