A brief firefight near the northern side of the Myanmar border, the route often used by drug smugglers, left 15 suspected drug dealers dead.
Thai soldiers killed 15 suspected drug smugglers as they attempted to cross into northern Thailand, army officials have said.
The altercation occurred near the 'Golden Triangle' - where Thailand, Myanmar and Laos meet - which has long been a hub for smuggling despite repeated crackdowns.
Rangers patrolling in northern Chiang Mai province encountered roughly 20 people walking from the direction of Myanmar, said an official from the Pha Muang Task Force, which monitors six border provinces.
Members of the group opened fire after they were ordered to stop for a search, the official said on Thursday, with the soldiers returning fire, leaving 15 dead.
Record meth seizures
Thirty bags of drugs were recovered from the scene, officials said.
"We did an initial check and found out that it was ice," a local army official said, following a search of the bags.
Ice is a street name for methamphetamine, a highly addictive stimulant often produced in Myanmar and shipped through Thailand and Laos for export around Asia.
Authorities across Southeast Asia have made record meth seizures in recent years.