Thai police have released a sketch of the main suspect in a deadly bombing that killed at least 20 people in the capital Bangkok, as the national police chief said the attack was carried out by "a network".

Police chief Somyot Poompanmoung said on Wednesday that the attacker did not carry out Monday's attack by himself, without elaborating further.

He made the comment as he headed into a meeting of national police commanders, adding that he was carrying orders from the prime minister who "is worried about the security of people and tourists in Thailand".

"He didn't do it alone, for sure. It's a network," Poompanmoung told the Associated Press.

Police say two other suspects have been identified in CCTV footage of the blast site.

Officials various times said that they did not rule out any group, including elements opposed to the military government, though they said it did not match the tactics of Muslim fighters in the south or "red shirt" supporters of the previous administration.

Foreigners dead

The sketch released shows a fair-skinned man with thick, medium-length black hair, a wispy beard and black glasses. It is unclear whether the man was Thai or a foreigner.

An image released by the Royal Thai Police on August 19 [Reuters]
The attack left at least 11 foreigners dead, with Chinese, Singaporeans, Indonesians and a family from Malaysia among the victims.

More than 100 other people were wounded by the blast that shredded bodies at one of the city's busiest intersections.

On Tuesday, the police released grainy closed-circuit television (CCTV) footage of a young man wearing a yellow t-shirt.

Police say the sketch could help locate the yellow-shirted man seen in the CCTV footage. A 1 million baht ($28,000) reward has been offered to anyone who can give police information leading to his arrest.

Police also said they would take the sketch to a court and ask that an arrest warrant be issued for a man matching the description.

Shrine reopened

On Wednesday, Buddhist monks led prayers for the reopening of a Bangkok shrine located in busy Ratchaprasong commercial district.

A small explosion on Tuesday by a bridge at the city's Chao Praya River has been tied to Monday's bomb.

Colonel Kamthorn Ouicharoen, of the Thai bomb squad police, confirmed the bridge bomb was the same type as the one detonated at the Erawan shrine.

Thailand has experienced a near-decade long political crisis that has seen endless rounds of street violence, but never anything on the scale of Monday's bomb.

Al Jazeera's Scott Heidler, reporting from Bangkok, said the bombings came just as tourism is rebounding in Thailand.  

"The arrival numbers of the all-important Chinese market doubled for the first half of this year compared to the same period last year," he said.

About 10,000 additional security forces have been deployed in Bangkok after the bombing, reassuring some tourists.

"At first I was shocked to hear about the blast. After assessing the situation, I think Bangkok might be safer after the bomb," one Chinese tourist told Al Jazeera.

Source: Al Jazeera and agencies