Thailand has said that a deadly bomb attack at a popular shrine in Bangkok was "unlikely" to be the work of international terrorists, but appealed for Interpol help in hunting a foreign man accused of being the prime suspect.

The military government was initially reluctant in asking for outside help in the investigation of the blast at the Erawan shrine on Monday evening that killed 20 people and wounded scores.

However, it has now sent the international police organisation a sketch of the suspected bomber.

An image released by the Royal Thai Police on August 19 [Reuters]

"We sent a request for assistance," Kissana Phathancharoen, deputy national police spokesperson, told Reuters news agency.

There has been no claim of responsibility and police have not determined a motive for the worst ever bomb attack in the Thai capital.

Thai police said that two men thought to have aided the prime suspect in the bombing were no longer under investigation.

The two men were suspected of shielding the suspected bomber while he planted the device.

But police spokesman Prawut Thavornsiri said one man who turned himself in was a tour guide, while the other man was a Chinese national who had already returned to China. 

'International terrorism unlikely'

The attack left at least 11 foreigners dead, with Chinese, Singaporeans, Indonesians and a family from Malaysia among the victims.

Thai military spokesman Colonel Winthai Suvaree said on Wednesday that the bombing was "unlikely to be linked to international terrorism".

He also said that Chinese tourists, who were among the victims, were not the "direct target".

Police suspect the young man caught in grainy footage leaving a backpack at the crowded shrine shortly before the explosion is foreign but Kissana said Thai police were not focused on any particular country or region with their appeal to Interpol.

"We basically sent in the modus operandi [of the suspect] and also the appearance of the suspect we're looking for," Kissana said.

Somyot Poompanmoung, a senior police officer, said on Wednesday that the attacker did not carry out the attack by himself, without elaborating further.

Officials 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.

Source: Al Jazeera and agencies