At 6.55pm yesterday in central Bangkok a bomb blast ripped through the heart of the city. The explosion — in Ratchaprasong near a Hindu Shrine, five-star hotels and busy shopping malls — seemed designed for maximum casualties. At least 19 people were killed and over 120 injured. 

There is much speculation about the actual target. While most initial reports said the bomb targeted the Erawan Shrine, that may simply have been a convenient place to deposit the device; two other bombs were discovered and defused nearby. 

There are two obvious possible perpetrators of the attack: rogue Red Shirt attackers or Malay separatists from the country's deep south. For both, the attack is outside their usual modus operandi in terms of scale and scope.

In recent months in Thailand's deep south, there has been a surge in improvised explosive device (IED) attacks. In July alone there were 27 IED attacks, according to Zach Abuza, a prominent researcher on the conflict. In April a car bomb ripped through a shopping mall car park in Koh Samui, a popular tourist island. This seemed to mark a new expansion of attacks outside of the normal area of operation for the insurgents. However, despite strong evidence to suggest the attacks were perpetrated by Malay separatists, the ruling Thai junta attributed the Koh Samui bombing to Red Shirt protesters. 

The conflict in Thailand's south is Southeast Asia's bloodiest (see Zach Abuza's excellent summary here). The conflict has raged for decades and in its latest and bloodiest installment has killed over 6400 people since 2004.

It is a conflict marked more by separatism than by religious extremism. The separatists are not akin to ISIS or Jemaah Islamiyah; rather, they are inspired by Sha'afi clerics wanting to retain their culture and fight off Thai cultural influence.  In recent years, however, there has been concern about the 'Islamisation' of the conflict in the deep south.

Unlike other civil conflicts in the region, the junta has shown no willingness to support a peace process. Instead, it seems to be striving for a military solution. The tougher line by the Government, which has included beefing up checkpoints and arming local paramilitaries, has restricted movement of insurgents and seen a decrease in casualties (between 2009-2014 this averaged 86 per month, between June 2014 and May 2015 this is down to 51 per month). The Government has no doubt made insurgent operations in the deep south more difficult. That tough line and a younger crop of hardline commanders is likely responsible for the recent increase in IED attacks in the South.

While Malay separatists are obvious suspects, the similarities of this attack to previous attacks attributed to Red Shirts cannot be dismissed. Police reports indicate that the device was a pipe bomb packed with 3kg of explosive and wrapped in a cloth. In February, two small pipe bombs exploded near Siam Paragon (close to yesterday's explosion), injuring two people. Those were blamed on Red Shirt protesters unhappy with the junta.  Red Shirt and anti-government protesters have previously shown their willingness to launch deadly attacks. During protests last year, M79 grenades were launched indiscriminately into camps populated by opposing protesters, and earlier this year a grenade was thrown at the Criminal Court.

Yet none of those attacks were as big or as targeted as yesterday's bombing. Miscalculation of the force of the explosion cannot, of course, be ruled out.

The junta's response will now come under scrutiny. To the surprise of many, the Government did not immediately go into lock down and install a state of emergency or strict martial law. But schools and businesses have been ordered closed today by Prime Minister Prayuth Chan-ocha.

A worrying long-term effect of the incident will be its impact on tourism. Since the junta took power in May 2014 tourism figures have been weak, angering the millions of Thais who rely on the tourism sector. In his initial statement, Defence Minister Prawit Wongsuwan was quick to note this concern: 'The perpetrators intended to destroy the economy and tourism, because the incident occurred in the heart of the tourism district.' 

The attack is an unsettling one for the junta. It promised stability. Now, under its watch, the largest and deadliest attack ever in Bangkok has taken place. How the junta responds will be closely watched and hugely important. A transparent investigation is unlikely. An all-out assault on Malay separatists or a rounding up of Red Shirt leaders is most likely the next move. That may be counter-productive. An opening of democratic process and inclusive governance would be a smarter and more effective way to tackle deep grievances in Thai society.