The violence, which saw tires set alight and dozens of electricity poles damaged by explosives, struck only hours after Thailand's king Maha Vajiralongkorn signed a new military-backed charter into law.
"There are 23 simultaneous incidents in three southern provinces and four districts of Songkhla," said Colonel Pramote Prom-in, an army spokesman for the south.
The region has sizzled with violence for over a decade as ethnic Malay rebels battle Thai troops for more autonomy, claiming more than 6,800 lives.
The new charter curbs the power of elected lawmakers and will bolster the army's role in government even after the junta steps down following elections which are expected in late 2018.
More From This Section
However Don Pathan, a Thai analyst based in the far south, said Friday's wave of attacks did not appear to be linked to the charter's signing.
The violence was most likely revenge for the killing of two suspected rebels by security forces last month, he told AFP.
Thailand has been hit by a string of suspected rebel assaults since that fatal shooting on March 29, including one that saw around 30 militants open fire on a police checkpoint in Yala province, injuring 12 officers.
The junta, which seized power in 2014, has held several rounds of talks with a group that claims to represent the insurgents.
But the negotiations have failed to make headway and many doubt the rebel negotiators have clout over fighters on the ground.