The pipe bomb found near an MRT station in Bangkok was potentially more dangerous than bombs that did go off earlier and could have caused injury, death and damage to people and property within a 10m to 20m radius, investigators said yesterday.
Prime Minister Prayut Chan-o-cha has ordered a thorough investigation as police looked at possible links to three other bombs that did explode in the Thai capital in the last two months.
Police found the pipe bomb in an overgrown lot behind the Thailand Cultural Centre subway station on Tuesday afternoon following a tip from a motorcycle taxi driver who went to fish in the area. They are now looking for two men who stopped by the area on a motorcycle before the bomb was discovered.
Investigators said the explosive was a black cylindrical steel tube with a screw cap measuring 20.3cm long and 7.6cm wide. It was packed with 220g of low-pressure explosives and could have been detonated by ignition or friction. The steel pipe was placed in a green basket inside a black plastic bag packed with cut metal, screws and nails.
Security had earlier been tightened in airports, train and subway stations in the Thai capital following a bombing on May 22 at the VIP waiting room in the military-run Phramongkutklao Hospital.
The blast, which happened on the day marking the third anniversary since the junta led by Mr Prayut came to power, injured 25 people.
Two smaller bombs earlier exploded in the historic part of the city, without causing serious damage - the first in front of the Government Lottery Office on April 5, and the second in front of the National Theatre on May 15.
The police have been criticised for their lack of cohesion in the investigation, giving different information to the media on the suspects.
But analysts said the blasts are meant to discredit the military government, whether they are politically motivated or related to the south Thailand insurgency.
"There could be more incidents of this nature in the future and they could become more and more violent," Mr Kan Yuenyong, executive director of the Bangkok-based think-tank Siam Intelligence Unit, told The Straits Times.
"Whatever the objective is and whoever may be behind them, they are sending a warning message to the government," he added.
Colonel Piyapong Klinphan, spokesman of the National Council for Peace and Order, asked for calm yesterday. He also dismissed any links between the pipe bomb that was recovered and the three previous bombings.