Only one civilian, identified publicly for the first time as Krissada Thibbadee, has been charged, with illegal possession of firearms and munitions. He is one of four civilians taken into police custody seven days ago.

Defence Minister Boonrawd Somtas said earlier that nine suspects had been released. Two of them were released in the afternoon and another seven later in the evening.

Boonrawd said there would be further investigation where police had failed to produce evidence to support a prosecution.

Prime Minister Surayud Chulanont, as head of the Internal Security Operations Command, will decide who handles further investigation.

"It could be the Department of Special Investigation that looks into matters not covered by the police," he added.

A police source said the nine suspects would be watched until police were positive they had no role in the attacks.

Another police source said three or four suspects would be charged with illegal possession of explosives soon.

Surayud described the latest information about the bombings given him by national police chief Kowit Wattana as "good progress".

"I think the police chief has shown dedication and made a considerable contribution to solving the case," he added.