Five Thai soldiers were killed in an attack at a checkpoint in the country's insurgency-hit south, the army said, one of the deadliest such incidents in years.

Six civilians were also wounded in the Wednesday evening attack in Narathiwat province, one of three Muslim-majority provinces gripped by a decades-long separatist insurgency, local officials said.

Members of Task Force Ranger Regiment 45 "were killed when assailants opened fire and threw pipe bombs at the Bukeh Sami checkpoint... while they were on duty protecting local residents", the army said in a statement late on Wednesday.

The public relations department of Narathiwat province said six civilians were hurt, adding that no group has yet claimed responsibility and no arrests have been made.

A low-level conflict has simmered in Thailand's southernmost provinces since 2004, killing more than 7,000 people, as rebels in the Muslim-majority region battle for greater autonomy.

Most attacks target security personnel.

The army paid tribute to those killed on Wednesday, saying: "Their service and sacrifice will be remembered and honoured with the highest respect."