Bangkok bomb well planned, involved more than 10 people: police

The deadly Bangkok bomb took over one month to plan and was executed by more than 10 people, the kingdom's police chief said Thursday, as more details emerged of the suspected network behind an attack that killed 20 people.

"This blast was made by teams," national police chief Somyot Poompanmoung told reporters, adding it would have taken about one month to plan Monday's assault on the busy shrine in downtown Bangkok.

Stating his belief that "more than 10 people" were involved, Somyot said the bomber would have needed several people to survey the site, plan an entry and exit strategy and acquire and make the bomb, which brought carnage to the Thai capital at rush hour.

"I believe this network has links with people inside Thailand," he added.

An unnamed foreigner has been fingered as the prime suspect after police released security camera footage of a young, bespectacled man in a yellow t-shirt leaving a backpack at the shrine shortly before the blast.

Authorities are looking for two other men seen on CCTV standing in front of the prime suspect as he deposits the backpack at the site of the bomb.

They leave the scene just before the suspected bomber walks away from the shrine.

Speculation has swirled about the motive and identity of the bomber and his supposed accomplices.

Thai police on Thursday said they are investigating areas of interest around the capital.

"From today (Thursday) we will go and 'x-ray' areas in and out of Bangkok," police spokesman Prawut Thavornsiri told reporters earlier, without explaining whether that would entail raids.