NO CLEAR TELL-TALE SIGNS

A composite picture taken from security camera and released by the Thai Royal Police showing a suspect who Thai police believes to be involved with the bomb attack walks with backpack (L) and leaves the Erawan Shirne (R) shortly before bomb exploding outside the Erawan Shrine in Bangkok, Thailand, August 17, 2015.[Photo/IC]

Police have not ruled out any group for the attack, including elements opposed to the military government, though they say it did not match the tactics of Muslim insurgents in the south or so-called 'red shirt' supporters of the previous administration.

Angel Rabasa, an expert on Islamist militancy at the RAND Corporation, said the attack could be the work of Islamic State, which has been expanding its reach in Southeast Asia, or an al Qaeda-related or independent jihadist group. However, such groups usually claim responsibility for their attacks.

Police said they were also considering the possibility that ethnic Uighurs were behind the bombing. Thailand forcibly returned 109 Uighurs to China last month.

Hundreds, possibly thousands, of members of the Turkic-speaking and largely Muslim minority have fled unrest in China's western Xinjiang region, where hundreds of people have been killed, prompting a crackdown by Chinese authorities. Many Uighurs have travelled through Southeast Asia to Turkey.