An M67 hand grenade was thrown into Ban Batu Mitrapap No 66 School in tambon Palukasamo of Narathiwat's Bacho district late Monday night and exploded, but hurt nobody, police said.
The attack occurred about 11.40pm. A team of forensic and bomb disposal police examined the scene on Tuesday morning.
The police said the grenade was thrown from outside the school on Narathiwat-Pattani road. The grenade hit a tree branch and dropped into a ditch along the fence. A loud explosion followed, but nobody was hurt.
The police believed the attack was intended to disrupt a ceremony on Tuesday morning to give certificates to kindergartan children who finished Level 3 of pre-elementary education. Despite the incident, the ceremony was held as scheduled under tight police security.