Prosecutors have appealed what they considered light prison sentences for individuals involved in a spiked drink scheme around a cram school area in Seoul’s Gangnam District.

The Seoul Central District Prosecutors' Office said on Wednesday that the appeal against the seven- to 15-year sentences was filed, citing an unjust weighing of an offense.

An official from the state investigative agency said those convicted had committed heinous acts by indiscriminately targeting youths for a drug crime with the distribution of laced energy drinks and blackmailing their parents for monetary extortion earlier in the year.

Last Thursday, the Seoul Central District Court sentenced one of the main suspects, identified by the surname Gil, to 15 years, and another suspect, a person surnamed Park who provided the methamphetamine, to ten years, while two others were sentenced to eight and seven years, respectively.

The group had colluded with a China-based voice phishing group to produce 100 bottles of the drink by mixing ten grams of methamphetamine with milk and offering them to 13 minors, claiming they were designed to increase concentration.

They then attempted to blackmail the parents of six of the students, threatening to report their children to authorities for drug use unless they provided hush money.