A record amount of drugs have been mailed to South Korea during the first three months of this year due to the brisk use of social networking services by dealers, customs authorities said Thursday.

Between January and March of 2015, some 3.6 tons of drugs entered South Korea by mail, an astronomical figure compared to 5.4 kilograms logged in the same period last year, the Korea Customs Service said.

There were nearly 70 different kinds of drugs worth a total 4.6 billion won ($4.2 million), an official of the service said.

Authorities attributed the massive amounts of mailed drugs to social networking services, which has become a common means of communication among drug dealers.

They said some mailers hid the drugs in electrical condensers on computer circuit boards or in Lego blocks.

Authorities vowed to intensify monitoring mail with the help of a new department at Incheon International Airport, South Korea's main gateway, that specializes in drug investigation.

The most common drug was Khat, a leafy green plant containing stimulants that is cultivated in North Africa and the Arabian Peninsula.

The people who brought it in were a 35-year-old Ethiopian woman and a 36-year-old American man.

The duo had tried to disguise the plant as henna, a plant used for temporary tattoos, and eventually shipped it on to the United States.

Other common drugs mailed here were marijuana, mixed drugs, methamphetamine and cannabis seeds.

Meth usually came from China and the Philippines, while marijuana and cannabis seeds usually originated in North America and Europe.

New types like the mixed drugs came from all over the world, including the Ukraine, the Netherlands, North America, Thailand, China and Japan. (Yonhap)