BANGKOK >> Police in Thailand said Thursday they made one of the country’s biggest ever seizures of illicit drugs, a haul including methamphetamine, crystal meth and heroin, with a total estimated street value of about 300 million baht ($8.2 million).

The police said the drugs were seized during a Wednesday night raid on a house in Nakhon Pathom, west of Bangkok, in which four men were arrested for possession of illegal drugs. They allegedly confessed to renting the house to stash the drugs before distributing them to dealers in the greater Bangkok area.

The seized drugs included 15 million methamphetamine tablets, 443 wrapped packages of heroin, 420 kilograms (926 pounds) of crystal meth and a quantity of drugs often used for partying, including “happy water” — a powder comprising several psychoactive substances to be made into a drink — and “five-five,” a strong sedative with the pharmaceutical name Nimetazepam, police said. The drugs were displayed to the media at a news conference.

The bust was the result of a two-year investigation initiated after another member of the trafficking gang was arrested, according to police. They did not say where the drugs originated, but U.N. and other experts have said that neighboring Myanmar is the source of most of the region’s methamphetamine and heroin.

“The Nakhon Pathom operation and seizure is no doubt significant, a huge result. But it is also a direct result of the security breakdown and expansion of the methamphetamine supply next door in Myanmar,” Jeremy Douglas, regional representative for Southeast Asia and the Pacific of the United Nations Office on Drugs and Crime, told The Associated Press. “We don’t see the situation improving, and more of these spillover events are likely.”

Myanmar has historically been the region’s main drug production area in part because of lax security measures in border areas where minority ethnic groups have long been fighting for greater autonomy. Some of the powerful ethnic armed groups there have been heavily involved in narcotics production for decades.

A 2021 military takeover in Myanmar that unseated the elected government of Aung San Suu Kyi triggered armed resistance nationwide, further destabilizing the country.

The U.N. drug agency’s June 2023 report on synthetic drugs in East and Southeast Asia warned that the huge trade in methamphetamine and other illegal drugs shows no signs of slowing down.

Another U.N. report in January noted that opium production has flourished in Myanmar since the military seized power, after many years of decline.