The attack occurred at dusk on Monday in one of the Thai capital's most popular tourism hubs, ripping through a crowd of worshippers at the Hindu shrine close to five-star hotels and upscale shopping malls.
Chinese, Hong Kong, Singaporean and Malaysian citizens were among the 21 people confirmed killed, with more than 100 injured as the blast sent a fireball into the sky and incinerated motorcycles.
Junta chief Prayut Chan-O-Cha on Tuesday branded the bombing the "worst ever attack" on Thailand, as he gave the first indications of who authorities believed were responsible.
"Today there is a suspect... we are looking for this guy," Prayut told reporters, adding the man was seen on closed circuit television at the blast site.
Prayut said the suspect was believed to be from an "anti-government group based in Thailand's northeast" -- the heartland of the kingdom's Red Shirt movement that opposes the military junta.
Bangkok has endured years of deadly political violence, with the junta ruling the nation since May last year after toppling the elected government of Yingluck Shinawatra.
The Red Shirts are a grassroots network of rural and urban poor that are loyal to Yingluck and her self-exiled brother, Thaksin Shinawatra, a populist politician who was a previous prime minister.
Prayut's comments suggest the investigation is shifting towards groups loyal to the Shinawatras, rather than Muslim militants from the country's far south where a deadly insurgency has raged for more than a decade.
No-one had claimed responsibility for the assault.
But Thai authorities said extensive CCTV footage had been of help at the start of their investigation.
Junta leaders also said the bomb was aimed at damaging the country's tourist industry, which is a rare bright spot in an otherwise gloomy economy, and tarnishing the junta's reputation.
"(The attackers) had the clear target of destroying our economy and tourism.... and discrediting the government," Defence Minister Prawit Wongsuwon told reporters.
Thailand's baht currency slumped to a more than six-year low on Tuesday and shares fell in Bangkok over concerns the attack could damage the tourism sector.
The blast site remained cordoned off early as bomb experts photographed the area scouring for clues, an AFP reporter at the scene said.
Police also tightened security across Bangkok, with hundreds of schools closed and checkpoints thrown up across the city.
The Erawan is an enormously popular shrine to the Hindu god Brahma but is visited by thousands of Buddhist devotees every day. Built in 1956, it is one of the Thai capital's top tourist attractions.
The bomb was detonated about 6:30 pm (1130 GMT) in the middle of the city's rush hour, sending a fireball into the sky as commuters and tourists fled in panic.
"I saw bodies lying on the ground and I saw vehicles on fire. I feel very sad and sorry that this has happened to Thai people," Panupan Chansing, 20, a hotel worker at the nearby Grand Hyatt Erawan, told AFP late Monday.
As dawn broke, Thais expressed fear for the coming days.
"I'm worried about Bangkok, I don't know what will happen next," one woman, who only gave her name as Rivewan, told AFP.
Islamic militants have carried out many attacks in other parts of Southeast Asia, including on Indonesia's holiday island of Bali in 2002 that killed 202 people.
But they have not made Thailand a prime target,
Authorities also appeared to downplay any link to the Muslim insurgents in southern Thailand where more than 6,400 people -- mostly civilians -- have died in the rebellion.
Government spokesman Werachon Sukhondhapatipak said the style of bomb -- which used three kilogrammes of high explosives -- was not similar to those used by the Muslim insurgents.
There has also never been a confirmed major attack by the insurgents outside the southern region despite the years of war.
Bangkok's power struggle has seen repeated rounds of deadly street protests and bombings for nearly a decade.
But none on Monday's scale.
Armed elements on both sides, in a kingdom awash with military-grade weapons, have been known to instigate unrest at key moments.
Many observers had predicted a fresh round of violence after the military seized power from Yingluck Shinawatra in last year's coup.
Thaksin Shinawatra, who was toppled by a 2006 coup, sits at the heart of the political divide.
Parties led by him, his sister or their proxies have won every election since 2001 thanks to the votes of the rural north and northeast.
But the clan are loathed by the Bangkok-based royalist elite.
Monday's attack drew quick expressions of grief from around the world. The US government released a statement warning its citizens to avoid the area, while also voicing sympathy for the victims.
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