The Gwangju High Court on Wednesday upheld a lower court ruling that sentenced two men to 10 years in prison for smuggling 12 kilograms of methamphetamine into the country.

The two suspects, Malaysian nationals in their 30s and 40s, were found guilty of violating the Act on the Aggravated Punishment of Specific Crimes, particularly the section on narcotics and psychotropic drugs.

"Considering the amount of smuggled drugs and severe nature of drug-related crimes, the sentence seems to be appropriate," the appellate court said in its ruling.

The defendants received the sentence from Jeju District Court on Feb. 1, after which they challenged the ruling, saying the punishment was excessive.

The two men were caught carrying methamphetamine at Jeju International Airport after an unidentified individual instructed them to do so in Malaysia in exchange for a cash reward. The reward was reported to be worth around 2 million won ($1,465).

The amount of drugs the men tried to smuggle in is estimated to be worth about 40 billion won, making it the biggest drug bust in the history of Jeju Airport.

Investigators found that the person who hired the men had given them specific instructions through a mobile messenger app, such as "go to the hotel directly after touching down on Jeju Island," "Don't be alarmed if the detection dogs (at the airport) bark at you," and "Just say (the drugs) are food."

The two suspects claimed that they did not know they were carrying drugs, but the court dismissed the claim.

This was based on the fact that they were asked to carry the packages, that their pay was substantially higher than the fee for conventional courier services and that their expenses for the trip were covered, as well as the fact that the messages they exchanged with their employer specifically included the word "powder."