The objects used as shrapnel, such as nails and bicycle wheel bearings, were of the same size and attached to the explosives by the same technique, he said.

The type of the explosive would be known by next week after confirmation by Australian explosives experts assisting police in the identification process.

Fingerprints were found on bomb materials at two sites - Gaysorn shopping plaza and the Pratunam Pier - but these had not matched any on police criminal records.

Initial findings showed that in terms of assembly techniques there were no similarities between the eight bombs and those used in the deep South by Muslim insurgents, Ek said.

Phaya Thai police have interviewed 19 witnesses from two sites where bombs went off - Victory Monument and Pratunam Pier, including 13 injured by the blasts. They reported seeing two potential bombers - male teenagers - at the first site, and one - also a male teenager - at the latter site.

Video footage from surveillance cameras near both sites did not detect any significant evidence in relation to the bombings.

Phaya Thai police chief Colonel Bundit Thisaphark said he had assigned both uniformed and plainclothes officers to keep an around-the-clock watch for more possible bomb attacks in crowded areas.

Prime Minister Surayud Chulanont, meanwhile, said he had asked police to find out those responsible for the bomb attacks as soon as possible.

Surayud refused to say what he discussed with Council for National Security chairman General Sonthi Boonyaratglin at a 30-minute meeting the two had at Government House in the morning.