Up to 1.3 million speed pills were seized from suspected drug runners with connections in Burma, Thai authorities said.
The authorities said they believe the gang smuggled drugs into Thailand over the Burmese border near Chiang Mai's Chiang Dao District, a rugged, remote mountain area populated by hill tribes.
The drugs were found hidden in pickup trucks, covered with bags of corn seeds, said an article in The Bangkok Post on Friday.
Another haul of 730,000 speed pills and 30 kg of crystal methamphetamine were seized from suspects in Chiang Rai, police said, also believed to have come from Burma through the northern Mae Sai District.
The suspects fled after an exchange of gunfire with police. No one was reported injured.
Mizzima reported recently that Burmese authorities are concerned that the illicit drug business in Burma is getting worse.
Burmese authorities have warned that the country's drug problem is “very dangerous” now.
“It's getting worse,” an official told Agency France Press. “Although the country has vowed to be drug free by 2014, it can only be opium free because of the problem of stimulant tablets.” Recently, Burmese authorities extended the date to be free of drugs by five more years.
Most of the illegal stimulant tablets are seized in the eastern border areas, with Shan State, which shares a border with Thailand, cited as a major source of narcotic shipments to Thailand.
Amphetamine production and poppy cultivation are one source of revenue for some armed rebel groups, say government officials.
Burma is the world's second-largest opium poppy grower after Afghanistan.