Thai police investigating Monday's deadly blast in Bangkok have said they are seeking a male suspect wearing a yellow T-shirt seen on closed-circuit television footage before the bomb went off at a Hindu shrine.

"The yellow shirt guy is not just the suspect. He is the bomber," a police spokesman told AP news agency on Tuesday.

Police have released CCTV footage showing the apparently young man walking with a backpack near the shrine. He then departed the site without it before the blast, which killed at least 20 people, including several foreigners, and wounded scores of others.

Other video footage posted separately on Thai media appeared to show the man sitting on a bench at the shrine, then taking off the backpack and leaving it behind.

The explosion occurred during the city's rush hour at the Erawan shrine, a Hindu place of worship that has become one of the Thai capital's top tourist sights, also attracting thousands of Buddhist devotees.

'Worst-ever attack'

Earlier, Thailand's junta leader Prayut Chan-Ocha said that security forces were looking for a suspect believed to be from an "anti-government group based in Thailand's northeast" following the blast.

"Today there is a suspect who appeared on CCTV, but it's not clear.... we are looking for this guy," Prayut told reporters, adding that the bombing was the "worst-ever attack" on Thailand.

Prayut also promised to track down those responsible.

The northeast region is a stronghold of the so-called "Red Shirt" movement, which opposes the military junta and remains loyal to ex-Prime Minister Yingluck Shinawatra, who was toppled in a coup last year.

Frequent unrest

Bangkok has seen repeated incidents of political violence since 2006, but Monday's blast was one of the rare occasions when foreigners, including Chinese, Hong Kong, Singaporean and Malaysian citizens, have been killed.

Thailand is also fighting a decade-long rebellion in its most southern provinces, home to a Muslim majority. The insurgency has killed more than 6,400 people, mostly civilians, but the Muslim rebels have never carried out a confirmed attack outside the southern region.

The comments by Prayut indicate that authorities are focusing more on groups loyal to the Shinawatra family, including Yingluck's self-exiled brother Thaksin Shinawatra, in their investigation.

Thaksin is living in self-exile after being himself ousted as prime minister in a 2006 coup. Parties led by members of the Shinawatra clan or its proxies ruled Thailand from 2001 owing to "Red Shirt" support from the rural north and northeast, but the royalist elite in Bangkok is hotly opposed to the family.

However, Red Shirts have so far carried out only relatively minor attacks on security forces or government buildings.

Second explosion

A second explosion shocked the city on Tuesday when a man threw a small explosive from Taksin Bridge in central Bangkok. The explosive landed in a canal without injuring anyone, according to police.

"If it did not fall in the water then it certainly would have caused injuries," said Colonel Natakit Siriwongtawan, the deputy police chief of Klongsan district.

Security camera footage showed people on the Sathorn Pier below the bridge being sprayed with water after the explosive blew up, with other bystanders running for safety.

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tj/jil (AFP, AP, dpa)