The clash occurred late Friday evening in a mountainous border area in the Mae Sai district of Chiang Rai province, part of the Golden Triangle region.
"Six bodies were found at the clash site along with seven bags of methamphetamines," Col Nattawut Yuwan, commander of the Mae Sai police, told AFP by telephone.
"We suspect they were hilltribe (Muser) people," he said, adding that the suspects had been travelling by foot and the clash happened quite close to the border with Myanmar.
There were no reports of any casualties among security forces.
Clashes between police and drug traffickers are fairly common in remote border regions.
The country has seen a marked increase in seizures of methamphetamine, which is relatively cheap and easy to make. It is often smuggled from Myanmar where armed rebels use profits from narcotics to fund their operations.