Four Muser tribesmen suspected of drug trafficking were killed in a clash with army rangers in Chiang Rai's Mae Fa Luang district early yesterday.
About 230,000 methamphetamine tablets were seized after the clash, the rangers said.
The exchange of fire took place about 8.30am as a group of rangers from the 31st Rangers Regiment of the Pha Muang Task Force patrolled a valley near Ban Armae on the Thai-Myanmar border in tambon Mae Salong Nok.
The rangers had been sent to the area after receiving information that a group of drug couriers would cross the border into Thailand with 1 million speed pills.
The patrol spotted the group of about 15 armed men, each carrying a backpack, about 2km north of the village.
When ordered to stop, the suspects opened fire, the rangers said. The firefight lasted about 15 minutes.
The bodies of two men in camouflage uniforms were found, along with two AK47 rifles and two backpacks, in a search of the area after the clash.
The rangers followed a trail of blood to the body of another man found with a backpack containing about 230,000 tablets, Capt Sumit Saenduangdee, commander of the patrol unit, said.
He said the traffickers were members of an armed Muser unit led by Lt Col Yi Se, whose arrest was sought with the help of a 2-million-baht bounty.