An academician in southern Thailand believes that the perpetrators of last night's bomb blast in central Bangkok are not from the country's separatist groups.

Dr Srisompop Jitpiromsi of Deep South Watch said the explosion, which killed at least 20 people, had nothing to do with the group responsible for the bombings in southern Thailand.

His reason was the type of bomb used was different.

"Thai police's initial investigation found nothing that can be associated with separatist groups in the south and before this, Bangkok was rarely a target of bomb attacks by separatists," he said.

Meanwhile, Thai authorities are looking for a suspect seen in a closed-circuit television (CCTV) footage of last night's incident.

Srisompop also believes that the main factor in yesterday's incident was internal political problem between the junta government and Red Shirt group.

However, he said, the theory was also difficult to accept because the Red Shirt members, who are Buddhists, were unlikely to do it.

"If we look at the area of the attack, it is near the shrine for Hindus and Buddhists (Erawan Shrine), which is regarded as highly sacred," he said.

Another possibility that could be associated with the incident is the good relations between Thailand and China.

"Recently, Thailand sent a number of Uighurs back to China, which was objected by Muslims in Thailand and also in Turkey," he said.

Srisompop added that the injured victims were mostly Chinese nationals.

He said whatever the theories were, the public should wait for the results of the police investigations.

Thai authorities today said they were looking for a man seen on the CCTV footage, who was wearing a yellow shirt and carrying a backpack, which was then left at the area.