Prime Minister Prayut Chan-o-cha is refusing to say whether domestic politics or international conflict lies behind the deadly bombing at the Erawan shrine.
As police Tuesday evening stepped up their hunt for a man filmed at the shrine shortly before Monday's deadly blast, sources say the probe is focusing on a revenge motive by Uighur militants, after the Thai government deported Chinese Muslim migrants to Beijing in July.
Speaking in a televised address last night, Gen Prayut would not be drawn on the motive, saying he did not want to cause public panic or mislead investigators.
The prime minister went before the cameras after a second blast went off at Sathon pier about 1pm Tuesday, which police said was designed to inflict heavy casualties.
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Assistant national police chief Prawut Thawornsiri said an improvised pipe bomb was thrown from Taksin Bridge, but hit a pillar and bounced into a canal where it detonated harmlessly.
Pol Lt Gen Prawut said he believed the perpetrator wanted to throw the bomb onto a busy walking platform leading to the pier but missed.
CCTV footage shows people running down a causeway over the canal to escape the blast.
Speaking on television, Gen Prayut sent his condolences to families of the victims killed and injured in Monday's blast at Ratchaprasong intersection, centred at the shrine, which killed 20 Thais and foreigners, and left 125 people injured.
"This incident shows us our country still has a person or a group of people with hostility to the nation operating actively," he said.
"They may be doing it for a political motive or to undermine the economy or tourism or for other reasons. The government will investigate and find the perpetrators and their accomplices as soon as possible," Gen Prayut said in the 10-minute address.
At a news conference earlier in the day, Gen Prayut declined to say whether the attack was perpetrated by Uighur militants as suggested by Chinese media and Thai police sources, but he urged the media to report responsibly and avoid causing panic.
"Whether this incident was motivated by domestic politics or an international issue, I don't want to give you an opinion because it could mislead investigators and cause panic," he said.
The bomb has already scared foreign tourists, with China, this country's biggest source of overseas arrivals, issuing a travel warning to its citizens.
Police sources said Uighur militants may have launched the attack in retaliation for Bangkok's decision to deport 109 Uighur refugees to China in July, which drew international criticism. Thai Muslim and human rights groups accused the government of separating the Uighur families by sending the male migrants to China and the women and children to Turkey.
Police deployed more officers to the Chinese embassy in Bangkok after its request two weeks ago. Intelligence from the Special Branch also suggested there could be an attack on Chinese tourists after Aug 11.
Meanwhile, police said they are hunting for a "Middle Eastern-looking man" caught on a closed circuit TV camera, whom they are "more than 50% certain" was the bomber. They are searching for the suspect in Nana sois 3, 5, 9 and 11, a neighbourhood popular with Uighur migrants.
The young, slightly built man wearing a yellow T-shirt and black-framed glasses, was carrying a backpack. He wanders around the shrine, and is seen sitting down and leaving the backpack there. Moments later he leaves the shrine and heads onto the street.
Police say he arrived in a tuk-tuk and left on a motorcycle taxi. They have asked the drivers to come forward. Police said the device which went off at the Erawan shrine, and the one at Sathon pier, were pipe bombs containing ball bearings. They were assembled professionally.
Pol Col Kamthon Ouicharoen, a bomb expert at the Metropolitan Police Bureau, said the first bomb was an improvised explosive device that looked like a model typically made abroad.
It was detonated by a timer similar to ones seen in Thailand in the past. But he said he found no connection to the bombs typically used in the deep South.
The Sathon bomb had a range of 30-50 metres, he said. "They aimed to inflict many casualties as that pier is frequented by many Thai commuters and foreign tourists," Pol Col Kamthorn said.
The police bomb squad found many 5-milimetre-diameter ball bearings scattered in the area, similar to those used by Iranian bombers found assembling a bomb in Soi Sukhumvit 71 on Feb 14, 2012.
