Thai authorities say they have the closed-circuit television (CCTV) footage of a suspect who is thought to be behind a bomb attack in the capital, Bangkok, that killed 20 people, including foreign tourists.

National Police chief Somyot Pumpanmuang said on Tuesday that the suspect, who was wearing a yellow shirt, was seen in a first CCTV image with a backpack at a popular Hindu shrine where the bombing happened.

The photos of the suspect released [Reuters]

Authorities said he was without the bag in a later one, adding that he could be Thai or a foreigner, and that a manhunt was under way.

"That man was carrying a backpack and walked past the scene at the time of the incident. But we need to look at the before and after CCTV footage to see if there is a link," Somyot told a news conference.

Police earlier said they had not ruled out any group, including elements opposed to the military government, for the bombing at the Erawan shrine on Monday evening.

However, the Thai army chief, General Udomdej Sitabutr, said the bombing "did not match the tactics" of Muslim rebels in the country's south.

The rebels, who Thai forces have been fighting for years, have rarely launched attacks outside their ethnic Malay heartland.

Worst ever attack

Thai Prime Minister Prayuth Chan-ocha said the bombing was the "worst ever attack" on the kingdom, and promised to track down those responsible.

"There have been minor bombs or just noise, but this time they aimed for innocent lives," Prayuth said. "They want to destroy our economy, our tourism."

Meanwhile, Defence Minister Prawit Wongsuwan said officials had no prior intelligence about Monday's rush-hour bombing of the shrine at a hectic intersection.

The Erawan Shrine is dedicated to the Hindu god Brahma, but is popular among Thailand's Buddhists as well as Chinese tourists. 

Six Chinese tourists were killed, Xinhua news agency reported.

There has been no claim of responsibility for the attack.

Police said 123 people were wounded and that the blast was caused by a pipe bomb.

Raising tension in the city on Tuesday, a small explosive was thrown from a bridge over a river without causing any injuries.

Police spokesman Prawut Thavornsiri said the blast at the Sathorn Pier frequented by tourist boats also was caused by a pipe bomb and could be related to the shrine attack.

Police said the bomb was thrown from the Taksin Bridge and fell into the Chao Phraya River, where it exploded. Security video showed a sudden blast of water over a walkway at the pier as bystanders ran for safety.

Al Jazeera's Wayne Hay, reporting from near the scene of the shrine blast, said Bangkok appeared to be "very much in shock" the morning after the attack. 

While the blast site has been cordoned off and security in the capital has been tightened, a state of emergency has not been imposed.

Thailand's junta leader said the bombing was the 'worst ever attack' on the kingdom [AP]

Source: Al Jazeera and agencies