The abbot of a forest monastery in Udon Thani province was shot dead while on the way back to the temple from his routine morning alms collection, police said.
Pol Col Santhan Intarachak, the superintendent of Muang district police, said the incident occurred shortly before 8am.
According to accounts from witnesses, Phra Bundhit Padhito, 48, the abbot of Tambon Sisiat forest monastery, was about one kilometre from the temple when he was followed by a group of men in a black pickup truck.
While on a dirt track through a rubber plantation, one of the men walked from the vehicle to the monk and fired two shots at him with a gun, hitting him in the chest. The monk was killed instantly.
Police are investigating the motives for the killing.
Phra Bundhit was a former director of Chaiwan Hospital in Chaiwan district of Udon Thani. He resigned from government service and went into the monkhood at the monastery about ten years ago.
A disciple of the late Luangta Maha Bua, Phra Bundhit had reportedly been a highly respected monk.