Narcotics police in Myanmar have seized a large amount of liquid fentanyl, providing the first evidence that the synthetic opioid is being produced in quantity in Southeast Asia’s infamous Golden Triangle region.

The discovery during a series of drug raids in Myanmar’s Shan state suggests a market for the drug has been created in the region, the United Nations Office on Drugs and Crime said Monday.

“Big international syndicates already active in the Golden Triangle are well positioned to take advantage of regional heroin demand and produce synthetic opioids alongside other drugs,” the agency's regional representative, Jeremy Douglas, said in a statement.

The U.N. agency warned that the development suggests that Southeast Asia is poised to become a significant source of synthetic drugs for other parts of the world.

“What has been unearthed through this operation is truly off the charts, and it is clear that a network of production facilities like those found would not be possible without the involvement and financial backing of serious transnational organized criminal groups,” Douglas said.

Massive amounts of methamphetamine and other drugs and their components were also seized in what the agency described as “one of the largest and most successful counter-narcotics operations in the history of the country and region.”

The Golden Triangle, a remote jungle area where the borders of Myanmar, Laos and Thailand meet, was once a major source of the world’s opium and heroin. In recent years it has also become a major producer of methamphetamine.

Fentanyl is a synthetic opioid estimated to be 50 to 100 times more potent than morphine and 30 to 50 times more powerful than heroin. It has been blamed for a large part of the waves of deaths from opioids that have swept through the United States in the past few years.

Experts say fentanyl is easier to make and smuggle than heroin, and far more profitable to sell. U.S. authorities accuse China, Myanmar’s northern neighbor, of being the source of fentanyl imported to the United States, a claim denied by Beijing.

The agency said the raids were carried out between Feb. 20 and April 9 in Kutkhai township of Shan state, in eastern Myanmar.

Shan state, like many border areas of Myanmar, is not tightly controlled by the central government, and armed ethnic minority militias and guerrilla groups hold sway over much of the territory.

The U.N. agency said without elaborating that “evidence of militia involvement was uncovered during the operation which resulted in the arrest of 33 Myanmar and foreign nationals.”

According to the agency, in addition to 3,748.5 liters (990 gallons) of methyl fentanyl, police seized 193.5 million methamphetamine tablets weighting 17.4 tons; more than 500 kilograms. (1,100 pounds) of crystal methamphetamine; 292 kg. (644 lb.) of heroin; 588 kg. (1,296 lb.) of opium; 49 kg. (108 lb.) of morphine; and 6.8 kg. (15 lb.) of ketamine.

Also seized were various precursor and pre-precursor chemicals used to make the drugs, along with sophisticated laboratory and production equipment.