Thailand's prime minister said Tuesday that authorities had seen "some suspects" in security-camera footage of the central Bangkok bombing that killed at least 20 people and injured 140, and promised to track down those responsible for what he described as the country's worst attack in history.

The defense minister, meanwhile, said officials had no prior intelligence about Monday's rush-hour bombing of a popular shrine at a hectic intersection. The blast from the improvised explosive device scattered body parts, spattered blood, blasted windows and burned motorbikes to the metal.

"This is the worst incident that has ever happened in Thailand," Prime Minister Prayuth Chan-ocha said. "There have been minor bombs or just noise, but this time they aimed for innocent lives. They want to destroy our economy, our tourism."

The explosion went off around 7 p.m. in an upscale area filled with tourists, office workers and shoppers.

"Today we have seen the closed-circuit footage, we saw some suspects, but it wasn't clear," Prayuth said. "We have to find them first."

Defense Minister Prawit Wongsuwan said the attack, which no one immediately claimed responsibility for, was aimed at destroying the country's economy by targeting a major tourist area.

"It is much clearer who the bombers are, but I can't reveal more right now," Prawit said, as he headed into a Cabinet meeting Tuesday morning. "We haven't ruled out terrorism."

He acknowledged that authorities had no idea an attack was planned.

"We didn't know about this ahead of time. We had no intelligence on this attack," the defense minister said.

Prayuth vowed to "hurry and find the bombers," though he noted there may be just one perpetrator. Speaking to reporters, he continued what has been a notoriously prickly relationship with the media since the former general took control of the government in a May 2014 coup.

Asked if there were leads on the suspects' identities, Prayuth bristled, "We are still investigating. The bomb has just exploded — why are you asking now? Do you understand the word investigation? It's not like they claim responsibility."

Early Tuesday morning, investigators surveyed the damage as police and soldiers guarded the area, still littered with shattered glass and other debris. The normally busy intersection that was closed off to traffic and eerily empty aside from onlookers standing behind police tape to take pictures. Barricades were set up outside five-star hotels in the neighborhood and security stopped cars to inspect trunks before letting them pass.

At least 20 people were confirmed dead and 140 injured, according to the Narinthorn emergency medical rescue center. China reported three of its citizens dead, and Somyot said a Filipino also was among those killed.

As a single, devastating blow to this Southeast Asian metropolis, Monday's bombing has no equal in recent history, though Thailand is no stranger to violent attacks. A more-than-decade-long insurgency by southern Muslim separatists has left more than 5,000 dead far from the capital. In Bangkok, politically charged riots centered on this very intersection in 2010 killed more than 90 over two months.

National chief of police Somyot Poompanmoung said the bomb was made with a pipe wrapped in cloth and weighed 3 kilograms (more than 6 pounds).

It detonated at the Erawan Shrine, which is dedicated to the Hindu god Brahma, but is extremely popular among Thailand's Buddhists as well as Chinese tourists. Although Thailand is predominantly Buddhist, it has enormous Hindu influence on its religious practices and language.

Throngs of tourists come there to pray at all hours, lighting incense and offering flowers purchased from rows of stalls set up on the sidewalk along the shrine. The site is a hubbub of activity, with quiet worshippers sometimes flanked by Thai dancers hired by those seeking good fortune, while groups of tourists shuffle in and out.

Bangkok has been relatively peaceful since a military coup ousted a civilian government in May last year after several months of sometimes violent political protests against the previous government.

At the same time, the military government has tightly controlled dissent, arresting hundreds of its opponents and banning protests. Tensions have risen in recent months, with the junta making clear that it may not hold elections until 2017 and wants a constitution that will allow some type of emergency rule to take the place of an elected government.

Stirring the pot has been exiled former Prime Minister Thaksin Shinawatra, who was ousted in a 2006 coup. It was his sister Yingluck Shinawatra who was ousted as prime minister last year.

Last week, Thaksin posted a message on YouTube urging his followers to reject the draft constitution because he said it was undemocratic. The draft charter is supposed to be voted on next month by a special National Reform Council. If it passes, it is supposed to go to a public referendum around January.

Another source of recent tension is the annual military promotion list, with the junta's top two leaders — Prime Minister Prayuth and Deputy Prime Minister Prawit — widely believed to be supporting different candidates. The reshuffle, which comes into effect in September, has traditionally been a source of unrest, as different cliques in the army, usually defined by their graduating class in the military academy, seek the most important posts to consolidate their power.

The U.S. Embassy in Bangkok issued an emergency message for U.S. citizens, advising them to avoid the shrine's area. In Washington, State Department spokesman John Kirby expressed deep sympathy to those affected by the Bangkok explosion. He said authorities were still determining whether any Americans were among the victims.

Tourists reacted with concern.

"We didn't think anything like this could happen in Bangkok," said Holger Siegle, a German who said he and his newlywed wife had chosen Thailand because it seemed safe. "Our honeymoon and our vacation will go on, but with a very unsafe feeling."

While bombings of this magnitude are rare in Bangkok, they are more common where Thailand's Muslim separatist insurgency has been flaring: in the country's three Muslim-majority provinces in the deep south.

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Associated Press journalists Grant Peck, Jerry Harmer, Michael Rubin and Penny Yi Wang contributed to this report.