Shootings and explosions are a near daily occurrence in Thailand's three southernmost provinces where more than 6,500 people -- the majority civilians -- have died since an Islamist rebellion against Thai rule re-ignited in 2004.
After months of relative calm that saw violence dip to a record low last year, there has been a palpable increase in attacks over the past few weeks.
The latest ambush occurred in Ra-Ngae district, Narathiwat province, with insurgents setting off a bomb as a police convoy passed by.
"Among the injured ones, four are seriously wounded", he added.
An AFP photographer on the scene saw a white truck riddled with shrapnel smashed into a tree with the bodies of three policemen still inside.
The insurgents are seeking greater autonomy from majority-Buddhist Thailand, which annexed the culturally distinct region more than a century ago.
The rebels employ brutal tactics including shootings, beheadings and bombings, often targeting perceived civilian collaborators such as teachers and Buddhist monks.
Earlier this month insurgents briefly seized a hospital and used it to launch an attack on nearby troops during a night of multiple coordinated assaults.
The Thai military also stands accused of routinely abusing human rights including torture and extra-judicial killings. The junta's vow to hold peace talks has borne little fruit.
Rights groups say peace is unlikely while a tight security net remains over the region.
Critics also cast doubt on the army's sincerity and the ability of their rebel interlocutors to control the revolt's foot soldiers.