Two troops were seriously injured when a bomb went off in Narathiwat's Tak Bai district Tuesday.
Wanchat Promraksa, a 2nd chief petty officer, and private Jenwit Kerdphra were injured.
The attack hit them shortly after they provided security escort to teachers.
An investigation suggests explosives of up to eight kilos must have been used in the attack.
Security officials believe this incident is also linked to the ongoing unrest.