Srivara also said a police review of CCTV recordings showed that a man had planted the bomb hours before the explosion, which led to two bystanders suffering minor injuries.

He said the small blast, which took place at 8pm inside a garbage bin in front of the old Government Lottery office, was aimed at creating chaos and panic in society rather than killing anyone because the blast radius was only one to two metres.

“Police officers are investigating the evidence. The bomb seems to have been assembled in a similar manner, so it is suspected the same old group did this,” he added.

Meanwhile, city police chief Pol Lt-General Sanit Mahathavorn expressed confidence that the culprits behind the explosion would be brought to justice soon. Following an urgent one-hour meeting at the Chanasongkram Police Station yesterday morning, Sanit said a police review of CCTV recordings in the area had been “useful” but declined to elaborate.

He also instructed police investigators to gather evidence and report back to him on this afternoon.

Sanit also urged members of public not to jump to conclusions or link the incident to politics pending the police investigation.

Sanit said he also instructed city precincts to boost security measures as a precaution.

He inspected the explosion scene again and expressed his opinion that the fragments found were similar to those found after a 2007 blast that damaged telephone booths in front of Major Cineplex Ratchayothin. No one was injured in that attack.

Police said they suspected the explosion was from a low-pressure pipe bomb and was aimed at creating chaos.

Earlier in the morning, police forensic officers along with the Explosive Ordnance Disposal team collected evidence at the scene, including metal pieces and an electrical circuit panel.