Bangkok police arrested 18 people and seized 30 motorcycles at Din Daeng intersection when protesters of the “Talu Gas” group converged there on Monday night.
Metropolitan Police Bureau deputy commissioner Piya Tawichai said on Tuesday that nine of those detained on Monday were minors.
Police would call their parents in for questioning. If they were deemed to have been negligent, those parents would face charges under the Child Protection Act, Pol Maj Gen Piya said.
He was adamant police acted within the law and international standards in dealing with the protesters.
There was no violence during Monday’s rally by Mr Nattawut’s group at Asok intersection, but police seized a vehicle equipped with a loudspeaker and arrested three demonstrators, he said.
However, the Thalu Gas group broke the law by blocking traffic, affecting other people. Some people also threw crystal balls, home-made bombs, pipe bombs, Molotov cocktails and firecrackers at government offices and private premises, he said.
There was arson at several spots around Din Daeng junction, he said.
A fire at an electrical control panel at the Din Daeng tunnel caused damage to the light control system, ventilation, water drainage and measurement systems, and closed-circuit camera system, Pol Maj Gen Piya said.
The Bangkok Metropolitan Administration’s department of drainage and sewerage was surveying the damage and would file a complaint against those involved, he said.
According to the MPB deputy chief, four groups of protesters planned rallies on Tuesday.
The Ramkhamhaeng for Democracy group, led by Nanthaphong Panmak, planned to gather in front of Government House at 10am.
The Car Mob group, led by Nattawut Saikuar, planned to rally at 4pm at Ratchaprasong intersection before heading to Asok intersection.
The Thalu Fah group planned to gather at 4pm at the Democracy Monument.
The other group, the Thalu Gas, planned to rally again at Din Daeng junction, said Pol Maj Gen Piya.