Busan Regional Customs said that it referred three foreign workers in their 30s to prosecutors on charges of smuggling the drugs, Wednesday.

Two of them are suspected of smuggling a synthetic drug known as spice by hiding it inside packaged snacks from October to November last year, and the other is suspected of smuggling 100 pills of MDMA hidden in cosmetics in July this year.

"We will reinforce drug investigation by strengthening analysis on small amounts of personal cargo such as international mail and express cargo,” said an official from Busan Regional Customs.

According to statistics from the National Police Agency, the number of drug offenders is on the rise. A total of 7,447 drug offenders were arrested by July this year, up 14.6 percent from the same period last year.

Meanwhile, the National Police Agency's National Investigation Agency said on Monday that it will extend the drug control period, which was expected to last until October, to December. A total of 932 drug offenders had been arrested as of Aug. 21 after an intensive crackdown began in early August.