The bomb hit the pick-up as it was carrying ten soldiers along a dirt road in Pattani province, leaving a pile of rubble and twisted car parts.
"The roadside bomb exploded before noon, killing six and injuring four," said Preuk Liengsuk, the police chief of Thung Yang Daeng district.
The Muslim-majority border region has been racked by violence for over a decade as ethnic Malay insurgents battle the government of Buddhist-majority Thailand for more autonomy.
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Frequent shooting and bomb attacks have claimed more than 6,800 lives since 2004, with both sides accused of rights abuses and atrocities.
Thailand's ruling junta has tried to restart peace talks with the Muslim militants since its 2014 power grab.
But the negotiations have failed to gain traction and regular attacks continue across the region.
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The Thai side is unconvinced that rebel negotiators at the table can control foot soldiers, while the insurgents do not believe the junta will concede political autonomy any time soon.
While the insurgents mostly target troops and police, they also routinely turn their weapons on teachers, local officials and other civilians seen as collaborators with the state.
The last major bombing blamed on rebels -- who rarely claim attacks -- left at least 40 people wounded outside a supermarket in Pattani in May.
The army has also faced repeated accusations of abuse, including extrajudicial killings and torture of detainees in a region ruled for years by emergency laws.
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