A "mastermind" gave the order for last week's wave of bombings and arson attacks, the Thai police said yesterday as their ongoing probe found several unexploded devices.
No one has claimed responsibility for the blasts that rocked tourist spots including Hua Hin and Phuket in southern Thailand on Thursday and Friday, which was a national holiday.
Deputy national police chief Pongsapat Pongcharoen told reporters yesterday the police know who the mastermind is but did not provide any details or motive.
"The events are connected, carefully planned and carried out across many areas and masterminded by one individual," General Pongsapat was quoted as saying.
The items found yesterday reportedly included mobile phones and power banks found in the Patong area of Phuket island and the seaside resort district of Hua Hin. Two more devices were found in Phang Nga, another popular tourist destination, on Saturday.
Mobile phones had been used to set off the explosions.
An oil rig worker was also arrested on Saturday in connection with the fire in a supermarket in Nakhon Si Thammarat province.
The police, working with his employer, arrested him at his workplace.
The attacks were the most serious in Thailand since the blast at Bangkok's Erawan shrine last year.
Eleven bombs went off in five provinces - Surat Thani, Trang, Prachuap Khiri Khan, Phuket and Phang Nga - while arson attacks took place in Krabi and Nakhon Si Thammarat.
Post-blast jitters have put locals on high alert.
Workers in Bangkok yesterday alerted the authorities to what eventually turned out to be a dud grenade in the capital's crowded Ramkhamhaeng area, according to local media reports.
Many analysts have suggested that the bomb attacks were related to the separatist insurgency in the "deep south", which refers to the Malay-Muslim-dominated provinces of Pattani, Yala, Narathiwat and a section of Songkhla.
Gen Pongsapat yesterday dismissed the suggestions, saying: "This has nothing to do (with)… the three provinces in the deep south," he said.
"As the national police chief (Gen Chakthip Chaijinda) said on the first day, this might be related to politics."
The bombings took place just days after a controversial draft Constitution was endorsed in a nationwide referendum.
Thailand has been ruled by a military government since a 2014 coup.