"This is likely the work of the insurgents [...] This is one of the biggest attacks in recent times", Colonel Pramote Prom-in, a regional security spokesman said, cited by Reuters.
There has been no immediate claim of responsibility for the attack, according to the media report.
Muslim Malay separatists are reportedly known to attack security personnel and monks in the southern Thai provinces which they see as territories occupied by a Buddhist-majority state.
The roots of the local conflict date back to the early 20th century, when the territory of the Pattani sultanate became part of mostly Buddhist Siam (former name of Thailand) and was separated into three provinces — Naranthiwat, Pattani and Yala.
Since then, Muslim movements in these regions have repeatedly called for broader autonomy and pushed for independence.