Police are expanding an investigation to find the mastermind of a group suspected of plotting unrest and possibly attacking key figures during festive events in Bangkok and the provinces.
The move came after soldiers arrested a former police officer and two civilians in Khon Kaen for conspiring to instigate unrest in Bangkok.
National police chief Chakthip Chaijinda said Wednesday that Pol Sgt Maj Prathin Chanket, who is a former police patrol officer, and two civilians -- Pisanu Phromsorn and Nutthapon Nawanlay -- have been remanded in military custody.
The three suspects are expected to be handed over to police for questioning today.
The suspects face charges of breaching Section 112 of the Criminal Code, known as the lese majeste law, and violating the Computer Act after authorities found them "hatching a plot to stir unrest in the city" and contacting each other about attack plans via the Line application, Pol Gen Chakthip said.
The arrests came after authorities discovered that a group of people in the Northeast were planning to cause chaos in Bangkok during the Loy Krathong festival, the King's birthday, the "Bike for Dad" event and during New Year celebrations, security sources said.
Pol Gen Chakthip said the group was found to have planned an attack involving important figures.
"We believe they are among those who are in opposition [to the government] but it is not clear yet if they are involved with any political group," Pol Gen Chakthip said.
"We don't know what the suspects' motives are. But what we do know is the suspects planned to target the Bangkok city area.
The "planned unrest" prompted Deputy Prime Minister Prawit Wongsuwon on Tuesday to order security to be tightened across Bangkok during several upcoming public holidays and festivities.