The Thai police have identified two more possible suspects in Monday's deadly explosion in downtown Bangkok, which has left at least 20 dead and more than 100 others injured, local media reported Thursday.

The two new persons of interests were seen in the same security camera footage that previously helped the police target a chief suspect, against whom an arrest warrant has been issued.

The footage showed that two males, dressed in red and white respectively, were standing close to the main suspect who was wearing a yellow T-shirt and glasses.

The police on Wednesday announced to offer a reward of 1 million baht (28,100 US dollars) for information leading to the capture of the main suspect. A sketch of the suspect was also released.

The police said that the suspected bomber was Caucasian, Arab or mixed race, and aged 20 to 30.

A motorcycle taxi driver who believed he had picked up the suspect after he left the explosion site, told a Thai TV station in an interview that the suspect spoke on the phone in neither the Thai nor English language.

But another motorcycle taxi driver was quoted by the Nation newspaper as saying that he used to pick up the suspect often in the morning, and the man spoke in both Thai and English.