"Security agencies have cooperated with agencies from allied countries and have come to the preliminary conclusion that the incident is unlikely to be linked to international terrorism," Colonel Winthai Suvaree, a spokesman for Thailand's ruling junta, known as the National Council for Peace and Order, told reporters on Thursday.
National police chief Somyot Poompanmoung said the attack took at least one month to plan and that at least 10 people were suspected of being involved in the bombing of the Erawan shrine in Bangkok, which is popular with locals and tourists. Twenty people were killed in Monday's attack on the shrine.
"This blast was made by teams," he told reporters. "I believe this network links with people inside Thailand... more than 10 people were involved."
Observers have speculated that the bomb may have been planted by extremists of the Uighur Muslim minority in China. Thailand deported more than 100 Uighurs back to China in July. Rights activists say they face persecution there.
Another police spokesman said that the main suspect - who police desbribed as a tall, fair-skinned foreigner speaking neither Thai nor English - may have left the country, but that police were "unsure" of his whereabouts. Police have released CCTV footage of a young man with glasses, wearing a yellow t-shirt and leaving a rucksack at the shrine shortly before the blast.
Two further men were seen standing next to the main suspect.
On Thursday, Thai police started investigating areas of interest around the capital. They have also asked Interpol for help with the investigation.
ng/jil (dpa, Reuters, AFP)