Authorities have asked Interpol for help in tracking down the man they believe planted the bomb in the Erawan shrine that killed 20 people, sending the international police organisation an image of the suspected bomber.
Initially reluctant to ask for outside help in the investigation of Monday's blast, deputy national police spokesman Kissana Phatsanacharoen told Reuters "we sent a request for assistance".
There has been no claim of responsibility and police have not determined a motive for the worst ever bomb attack in Thailand.
Police suspect the young man caught in grainy footage leaving a backpack at the crowded shrine shortly before the explosion is foreign, but Pol Lt Col Kissana said Thai police were not focused on any particular country or region with their appeal to Interpol.
"We basically sent in the modus operandi (of the suspect) and also the appearance of the suspect we're looking for," Pol Lt Col Kissana added.
Prime Minister Prayut Chan-o-cha initially said the attack was Thailand's problem and should be resolved internally.
Police have issued an arrest warrant for an "unidentified foreign man" in a yellow shirt seen in the video footage and have said investigators believe two other men seen on the footage were accomplices.
"We are confident at least three people were involved in this, but maybe more," Pol Lt Col Kissana said.
Checks at airports and other exit points found that no one matching the description of the main suspect had left the country since the attack, he said.
