Most of the 20 people suspected to be involved in Thailand's latest round of bomb and arson attacks, which killed four people and left scores injured, were from the southern provinces, police chief Gen Chakthip Caijinda confirmed today.

Despite this, the police will not pin conflict in southern Thai as the motive behind the attacks as they were also investigating other motives for the violence, he told the media when met at the Royal Thai Police's building in Bangkok.

He said that if the latest spate of attacks was motivated by the southern Thai problem with an aim to expand the conflict beyond the deep south, it could have occurred a long time ago.

"We do not rule out any motives for the attacks, such as referendum, area expansion of southern border conflict or special mission for someone. We do not rule out anything yet," he said.

He pointed out that the type of clothes the suspects wore when carrying out the attacks - short pants with their faces and hand covered - were also different from militants in the deep south.

Besides that the suspects also acted like tourists, the chief police said.

He said that the authorities have been making good progress on the investigation including on the suspects' assembly point, their travelling route before and after conducting their mission.

Currently the police were investigating the suspects' "money trail," he added.

"I know all of their steps during this mission," Chakthip stressed.

He also said that the 20 people who were involved in the clandestine mission came from the "younger generation" and this explained the scant details the authorities have on the suspects.

- Bernama