Authorities have tightened security measures across the country after a car bomb rocked a Koh Samui shopping mall at the start of the busy Songkran holiday.
The explosion late Friday night in a parking lot at Central Festival Samui resulted in minor injuries to seven people and damaged 10 cars as well as other mall properties.
The pickup containing the bomb had been stolen in Yala, leading to early speculation that the incident was linked to the insurgency in the three southern border provinces.
But a government spokesman was quick to steer the speculation in another direction, saying the attack might be linked to incidents earlier this year in Bangkok.
"Initial reports back the theory that [the Samui bombers] are the same group that created bombings in Bangkok," said Maj Gen Sansern Kaewkamnerd.
He declined to elaborate on the basis for the theory. Police have several people in custody in connection with the two Bangkok incidents: an explosion in a transformer near Siam Paragon on Feb 1, and another in which a grenade was lobbed into the empty parking lot of the Criminal Court building late on March 7.
"As authorities have taken strict precautions [in Bangkok], situations are being created elsewhere. Authorities have found some links with incidents in Bangkok and are tracing suspects from clues in the scene," Maj Gen Sansern said.
Suspicions about a political motivation have been rife because the Samui blast took place just a half-hour after a major fire began on the Surat Thani mainland on Friday night. The blaze caused 50 million baht in damage to the Surat Thani Cooperative founded by politician-turned-monk Suthep Thaugsuban. Mr Suthep led the anti-government protests that culminated in the military coup last May.
Authorities step up security measures in downtown Hat Yai district of Songkhla following the Samui explosion. (Photo by Vichayant Boonchote)
Samui airport has banned overnight parking and tightened security checks of all vehicles and passengers in response to the incident at Central Festival.
Maj Gen Sansern said Prime Minister Prayut Chan-o-cha had ordered security authorities to maximise their measures in light of Friday's incidents.
If the alleged Bangkok bomb plotters were indeed behind the Samui attack, they might have needed help from people with far greater expertise in rigging cars to blow up and triggering explosions from mobile phones. That led to a second theory, advanced by Col Banpot Pulpian, a spokesman for the Internal Security Operations Command (Isoc).
"It is possible that the culprits are members of a violent group in the southern border provinces or experienced car bomb makers in the southern border provinces and they were hired by some party for another purpose," he said.
He said the Samui blast had some of the hallmarks of an incident in Ramkhamhaeng Soi 43/1 in Bangkok on May 26, 2013. In that incident, a bomb exploded in a pile of garbage in front of a beauty salon, injuring seven people. The bombers came from the southern border provinces of Narathiwat and Pattani.
However, he also noted that Isoc's intelligence had not found evidence that the southern insurgents wanted to expand their campaign of violence outside their home region.
The Mazda Fighter pickup used in the Samui attack had been reported stolen in Yala on March 31. Eight robbers had taken the vehicle from an official of the Tambon La-ae administrative organisation in Yaha district.
Thai media reported that the vehicle's owner was being held at a paramilitary ranger base in Yala for interrogation. Authorities were quoted as saying the man had given "contradictory testimony" about the incident and not provided any useful information.
PM's Office Minister Suwaphan Tanyuvardhana, a former director of the National Intelligence Agency, said authorities could not conclude yet whether the Samui incident was politically motivated.
Intelligence officials earlier had recommended precautions at tourist destinations, he added.
Col Winthai Suvari, the spokesman for the National Council for Peace and Order (NCPO), said that Gen Prayut, the NCPO chief, and Gen Udomdej Sitabutr, the army chief and NCPO secretary-general, had ordered soldiers and police to intensify security measures, especially at night.
"I admit that some parties continue to find chances to create disturbance in the society. ... This goes against the will of the majority of people who want social order," Col Winthai said.
While the vehicle used in the Samui bombing originated in Yala, those who study the southern insurgency note that attacks outside the three border provinces are extremely rare.
The only exceptions have been a handful of attacks in neighbouring Songkhla, focused on the busy commercial centre of Hat Yai.
Authorities in Songkhla on Saturday stepped up the already stringent security measures in place for Songkran following the Samui incident.
A combined team of soldiers, police and security volunteers set up checkpoints on roads leading to central areas of Hat Yai. They concentrated their efforts on spotting any vehicles that had been reported stolen and might be used as car bombs.
Patrols were concentrated at seven major commercial spots in central Hat Yai, especially around the venue where the Midnight Songkran event is to be held at Nipat Uthit 3 and Saneha Nusorn Road, looking for suspiciously parked cars.
Security officials also conducted thorough inspections of vehicles before allowing them to park at all shopping malls. The checkpoints will remain in place outside the centres' normal operating hours.
Central Pattana Plc closed its Hat Yai branch on Saturday to wait for an assessment of the security situation by authorities.
Saran Tantichamnan, the general manager of Central Festival Hat Yai, said security cameras at Central Festival on Samui had captured a person suspected of involvement in the Friday night attack. The damage including lost business opportunities could not be estimated yet, he added.
Soldiers and police along with bomb-sniffing dogs were present at Central Festival Hat Yai to ensure safety for shoppers, Mr Saran said, adding that the centre would reopen on Sunday if authorities deemed conditions safe.