There was wide sharing on social media of a report about "a white foreigner" who arrived in a tuk-tuk carrying a rucksack, and then was seen without it. Later the bomb went off. However, Pol Lt Gen Prawut said it was still unclear who the bomber could have been.
He said police would need some time to collect evidence, which was different from the Paragon bombing in February which involved only a low-power device.
Police on Tuesday morning swept the streets in the Ratchaprasong area for possible evidence. The intersection remained closed, causing traffic jams in the area, but was expected to reopen about noon on Tuesday.
Pol Lt Gen Prawut said the bomb blew debris and shrapnel up to 100 metres from site of the explosion.