Rubber plantation workers Jad Suwanchatri, 52, and his wife, Serm, 51 - both Buddhist defence volunteers - had stopped their motorcycle to clear a log from a road in Yala province when unidentified assailants shot the couple and then cut their throats, police Lieutenant Somporn Ritthirat said on Friday.
Thai police said it was unclear exactly when the workers were killed, but they were notified early on Friday morning.
The upsurge in killings caused widespread fear and prompted many workers to stop tapping rubber at night, when the work is usually done, and go out in the morning instead.
Also on Friday, two unidentified armed men fatally shot Kobkua Ransaewa, the principal of a public school in nearby Narathiwat province, while she was riding a motorcycle away from the school at lunchtime. The school was temporarily closed after the incident.
Continuing violence has claimed the lives of more than 880 people since January 2004 in Yala, Pattani and Narathiwat provinces.
The unrest has largely been attributed to the return of a decades-old Muslim secessionist movement thought to have faded after a government amnesty in the 1980s, according to government officials.
Southern Thai Muslims have long accused the government of neglect and unfair treatment, mainly in jobs and education.
About 80 people suffocated to
death while in custody last year
Rights groups and a Thai government-appointed independent commission have also accused the government of heavy-handedness in dealing with the south.
The commission was set up in order to investigate the deaths of about 80 people by suffocation in the south while in police custody during an alleged protest on 25 October 2004.
Differentiation between areas
Defence Minister General Thammarak Isarangura Na Ayutthaya said on Thursday that the government will "somewhat adjust" its policy in the south by differentiating between "battle areas" and "peaceful areas," according to the Thai News Agency.
"We will identify areas where urgent attention is needed," he was quoted as saying, without elaborating.
The defence minister was not immediately available for comment.
General Suraphan Phumkaew, the chief army spokesman, said the plan would start in August, and that Yala province's Betong district - where defence volunteers have received training from security forces - would be named the first "peaceful" district, TNA reported.
Another army spokesman, Colonel Somkuan Saengpatranetr, said earlier that the army was considering rewarding the peaceful villages by promoting their officials.