Coordinated attacks in insurgency-plagued Cho Airong district of Narathiwat province on Sunday were carried out by factions of the separatist Barisan Revolusi Nasional (BRN) group opposing peace talks, according to authorities.
Lt Gen Nakrob Boonbuathong, secretary to the Thai team involved in peace talks with the southern insurgency umbrella group Majlis Syura Patani (Mara Patani), said the attacks were undertaken by hard-core BRN factions.
Citing information provided by group members, he said the hardliners carried out the attacks in a symbolic move to mark the 56th anniversary of the BRN on the same day.
He said the BRN conceded it cannot control all of its factions and Thai authorities will raise the matter at talks with the BRN next week in Malaysia.
The security flare-up is expected to be addressed in the terms of reference (ToR) in the peace deal to be signed by both sides in the future.
The BRN's hardline factions appear to have stepped up resistance to the peace deal, Lt Gen Nakrob said, adding he wanted security officers to stay vigilant.
National police chief Chakthip Chaijinda said the three attacks in Cho Airong district include one at the Cho Airong Hospital when up to 50 armed men emerged from a forest and laid siege to a two-storey building and three accommodation units for medical practitioners in the hospital compound on Sunday morning.
Before retreating, the insurgents fired a barrage of gunfire at a military ranger depot nearby. More than 500 shells of M16 and AK-47 assault rifles were found at the scene.
Police have not released the identity of the attackers.
He denied the assailants have links to an Islamic State-affiliated organisation called Black Swan, which former prime minister Chavalit Yongchaiyudh claims has infiltrated the far South.
Meanwhile, Prime Minister Prayut Chan-o-cha has ordered officers to tighten security in the far South in the wake of the attacks.
Government spokesman Sansern Kaewkamnerd said Gen Prayut instructed the officers to ensure security in crowded areas and car parks.
He also ordered security authorities to arrest the attackers quickly.
"The government will not tolerate behaviour that is in contempt of the law," Maj Gen Sansern said.
"Efforts will be made to urgently suppress terrorists, influential figures, drug and contraband oil traders and human traffickers in a crackdown which should yield results within six months," he said.
Meanwhile, Col Pasit Chanlekha, chief of the 46th paramilitary ranger regiment who took an army team to inspect the scene of the Sunday mayhem, said the attacks in Cho Airong were headed by key insurgent figures, Lukman Latebue-ring and Suedi Putei.
After a video conference with staff from Cho Airong Hospital, where one of the attacks took place, Public Health Minister Piyasakol Sakolsatayadorn said the staff were in good spirits. He said more lighting equipment and CCTV cameras will be installed at the hospital.
The National Human Rights Commission yesterday denounced the attacks, including the one at the hospital.
Police were also investigating a gun attack, also on Sunday, on a police apartment building at Lammai police station in Yala's Muang district. Multiple bullet holes were found.