Two Hmong men were cut down in a hail of gunfire and a Hmong woman was injured by a stray bullet during the Hmong New Year festival in Phetchabun on Monday night.
Police said the shooting occurred as the fair was underway at a football field in Moo 4 village in tambon Khek Noi in Khao Khor district.
The slain victims were identified as Jia Ritthinetiul and Sa-ngiam Jermsungnone.
Aroonrat Sae-her, 21, was hit in her left arm by a stray bullet.
Witnesses told police that a man with a facemask walked up to Jia and Sa-ngiam and strafed them with an assault rifle before fleeing the scene.
Police suspect the shooting was motivated by a conflict over drugs.