South Korea deports alleged Thai drug kingpin

South Korean authorities deported to Thailand on Tuesday a man accused of running a major drug trafficking operation who had evaded arrest for years, Seoul's spy agency said.

The 43-year-old Thai suspect was arrested on Monday at a hotel in Seoul's affluent Gangnam district at the request of Thailand's Office of the Narcotics Control Board, South Korea's National Intelligence Service (NIS) said.

Thai authorities had issued some 50 arrest warrants over the past decade in a bid to apprehend the suspect, whose name was withheld, the NIS said.

Authorities described the scale of the narcotics operation as "unprecedented" for a single organisation, involving 11.5 tonnes of methamphetamine, five tonnes of ketamine and 271 million pills of "yaba" -- a potent mix of methamphetamine and caffeine -- over 25 years.

The suspect's organisation is believed to have trafficked narcotics across Thailand and another country, according to the South Korean spy agency.

The NIS said the methamphetamine linked to the alleged kingpin was enough to supply up to 380 million people, putting the total value at 4.6 trillion won ($3.1 billion).

The volume of ketamine -- an anaesthetic that can be used as a party drug -- was enough for 100 million people, it added.

The suspect had entered South Korea legally using a third-country passport, the NIS said.