The ambush came a day after a Muslim man attending his son's wedding was shot and killed by attackers riding motorcycles.
The attacks come amid a spike in violence during a five-year insurgency in the area that has left at least 3,700 people dead.
Since last month, at least 40 people have been killed and more than 100 wounded in violence in the region.
The deadliest recent incident was the killing of 10 Muslims at a mosque in Narathiwat in early June.
Most of the violence in Thailand's south has been blamed by authorities on Muslim armed separatist groups.
However, no group has claimed responsibility for the latest attacks.
The fighters in Thailand's southern provinces have not specifically stated their motives, but they are thought to be fighting to establish an independent state in the three Muslim-majority provinces.
The latest rebellion in the former ethnic Malay sultanate began in January 2004 when fighters raided an army base, killing four soldiers.