The Phra Phrom statue shows blast damage. Sakchai Lalit / AP

Authorities said they were keeping watch for the suspect at the country's borders, but Somyot Pumpanmuang said that it was not clear how many people were involved in the attack or if they were still in the country.

"I don't suspect one person, I suspect many people," he said. "I am confident that there are Thais involved but I am not saying it is just Thais or that there are foreigners."

Police have released still photos of the man, both with and without the backpack, and a video posted separately on Thai media appeared to show the same man sitting on a bench at the shrine, taking off the backpack and leaving it behind as he walked away.

"The yellow-shirt guy is not just the suspect. He is the bomber," police spokesman Lieutenant General Prawut Thavornsiri told The Associated Press on Tuesday.

The attack has raised concerns about safety in a city that draws millions of tourists and had never experienced an attack of this magnitude.

AP - Reuters - Xinhua