Rescuers said divers and village volunteers found the body of Subear Dallah, 22, in the river on yesterday morning after searching for him since Tuesday, reports the Bangkok Post.
The man used a boat to illegally enter Kelantan state from Sungai Kolok district in the southern province on Tuesday. When Malaysian police spotted him on the river bank, he decided to swim back to Thai territory for fear of getting arrested.
Rescuers were alerted after people saw him disappearing into the water.
The autopsy on his body is being conducted at Sungai Kolok Hospital.
Malaysian security authorities have stepped up measures to clamp down on people illegally entering Kelantan as part of a campaign against border crimes that included an idea to build a wall along the river.
However, the proposal was rejected by Malaysian Home Minister Saifuddin Nasution Ismail in Kuala Lumpur on Thursday.