A leader of Thailand's so-called "red shirt" opponents of the military junta has offered a reward of 2 million baht (S$79,100) for information on the suspect behind the fatal bomb attack on Bangkok's Erawan Shrine on Monday, according to the Bangkok Post.

This is on top of the 1 million baht offered by the Thai police for information that would lead to the perpetrator's arrest.

United Front for Democracy against Dictatorship (UDD) leader Somwang Assarasee, who was a secretary to ex-deputy commerce minister Nattawut Saikuar, told the newspaper that he would hand the reward to the informant himself.

Mr Somwong, who owns an electrical appliance company, added that he was offering the reward as the attack had harmed Thailand seriously, the Post reported.