Evidence from a dead militant prompted marines to prepare for a raid from southern insurgents in the early hours of Wednesday, which led to heavy losses to the attackers, a naval officer said.
Capt Thammanon Wanna, chief of Narathiwat Task Force 32, said security authorities were on alert for a possible large attack after intelligence analysts found a map of the base and other documents on the body of Suhaidee Tahe, a 31-year-old militant killed last Saturday.
Suhaidee was already on the most-wanted list of southern militants, as officials believed he was involved in the notorious murder of school teacher Chonlatee Charoenchon, shot to death in front of students and staff at the Ban Tanyong School canteen in Bacho district, Narathiwat, on Jan 23.
About 60 attackers armed with M16 and AK47 rifles arrived at the marine base in two pickups and two motorcycles to start the attack at 1:10am Wednesday. Task force marines manning the Ban Yueror base in Bacho were supposed to be asleep, according to the attackers' plans. Instead, the troops were on full combat alert.
Within 20 minutes, the insurgents had suffered about 20 per cent dead without inflicting a single marine casualty. The attackers turned tail, leaving behind blood trails of their wounded.
The assailants wore military-style, camouflage uniforms, possibly stolen or purchased, and bullet proof vests, which appeared to be stolen from government stocks for volunteer workers in the South.
Among the dead was Maroso Chantrawadee, a key local leader of the Runda Kumpulan Kecil (RKK) militant group, with a two-million baht reward on his head and also wanted in the death of the teacher in January.
Maroso's last days clearly were on borrowed time. On Jan 11, he narrowly escaped from a clash with army rangers in Bacho, but he was not so lucky on Wednesday. He was among 16 attackers died in the raid.
Security forces also seized three hand grenades, three homemade bombs, 13 riffles, three pistols, one pickup, two motorcycles and a chainsaw, Col Pramote Promin, spokesman for the 4th Region Forward Command of the Internal Security Operations Command, said. No marines were killed in the intense battle, but there was no word on whether any were wounded.
The seized pickup had been reported stolen from Khok Pho district in Pattani on Dec 6, he added.
Security forces saddled up and began hunting insurgents fleeing the scene, as Fourth Army chief Udomchai Thammasarorat asked residents to stay inside to help troops track and find the fleeing insurgents.
Marso Chantrawadee, RKK leader and most-wanted insurgent, killed in the assault.
Lt Gen Udomchai called for understanding from locals on the curfew as it would clear the way for security forces to comb the area and go after the fleeing militants.
Security measures were stiffened in all key positions in Narathiwat, Pattani, Yala and part of Songkhla, due to concern about retaliation by militants after suffering such a huge loss.
Defence Minister Sukumpol Suwanatat also ordered a probe on bullet proof vests worn by the assailants. The vests were handed out by authorities to defence volunteers, he said.
Prime Minister Yingluck Shinawatra, ACM Sukumpol and the opposition leader Abhisit Vejjajiva all praised the marines for their combat readiness in repelling the attackers.
"It is notable that some of the attackers carried a rope and some wire, which might have been intended for use in capturing some marines and holding them hostage," the defence minister said.
Officials also showed sympathy for families of the dead insurgents, and the prime minister promised financial help for them.
The curfew made Bacho and Mai Kaen districts quiet on Wednesday. All markets were closed and vehicles were thoroughly checked by authorities searching for the militants.
Mareeya Kaseng, a food vendor in Mai Kaen, said the curfew affected her work and hoped that it would end at dawn Thursday as promised.
Explosives expert examines the body of one of the dead attackers, wearing military combat fatigues and a bullet-proof vest which authorities believe were stolen from civilian volunteer workers in the South.