Two days after a powerful bomb blast left at least 20 people dead in the heart of Thailand capital Bangkok, the Thai police have released a sketch of what the suspected bomber looks like.

The suspect, wearing a yellow T-shirt and shorts, was seen on CCTV footage dropping off a backpack at the Erawan Shrine. However, his face was not clear in the footage.

"The yellow-shirt guy is not just a suspect. He is the bomber," Police Lt. Gen. Prawut Thavornsiri  told The Associated Press.

The authorities also announced a reward of 1 million baht ($28,080) for any information about the suspect. 

The police have now released a more detailed sketch of the suspect, which shows a young man with spectacles and thick black hair. 

Here is a photo of the police sketch - 

The police have also said that the bomber did not act alone and was possibly 'part of a network'. 

They have reportedly identified two other men seen in the CCTV footage as suspects, Reuters reported. 

The suspected bomber was seen in the CCTV video, sitting with a backpack, before he casually leaves it at the site and walks away minutes before the blast. 

The Bangkok bombing, which killed more than 20 people, including several foreign tourists, on Monday, is said to be the deadliest strike in the popular tourist destination. 

The moment the horrific bomb blast occurred was also caught on CCTV.