Thai police will not rule out anything in their investigation into last night's explosion, which they now believe was caused by a pipe bomb and intended to create chaos.

Bangkok police chief, Lt Gen Sanit Mahathavorn who inspected the scene of the incident today, said the authorities would not discount any motive in their pursuit to find the truth.

"We need to have complete evidence before concluding the case. Do not rule out anything on the motive," he said on last night's incident in front of the old Government Lottery building in Ratchadamnoen Road at 8pm (local time).

The explosive device was hidden in a trash bin and went off just as two City Hall workers were working nearby, causing both to suffer slight injuries and were sent to a nearby hospital for medical attention.

According to Sanit, the authorities were also reviewing the nearby closed- circuit television cameras (CCTVs) to find any clue on the explosion and the perpetrators.

The CCTV recording had been useful in the investigation, he said.

Meanwhile, a member of the police's Explosive, Ordnance and Disposal (EOD) unit at the scene, said they found shrapnels related to the pipe bomb which caused the explosion.

The explosive device, he said, was made from a PVC pipe.

Immediately after the incident last night, police at first thought the explosion was caused by a "Ping Pong Bomb", a crude explosive device that is easy to assemble.

"The explosion was more intended to create chaos among the public, rather then to inflict death and injuries," said one of the policemen.

-- BERNAMA