Police have reportedly detained two men for questioning in a string of bomb blasts that rocked five southern provinces on Thursday and Friday, killing four people and injuring 35.
No other details were available about the men being questioned, and senior law enforcement officials continued to insist that the incidents were acts of "local sabotage" and not terrorism.
Pol Maj Gen Piyaphan Pingmuang, deputy spokesman for the Royal Thai Police, said Thailand had no conflicts related to race and religion among ethnic minorities and faced no threats linked to Islamic State (IS) terrorism.
The blasts -- in Prachuap Khiri Khan, Phuket, Trang, Surat Thani and Phangnga -- also had no links to unrest in the three southern border provinces of Yala, Pattani and Narathiwat, he added.
The explosions stemmed from internal conflicts and were aimed at creating chaos, said the deputy police spokesman, echoing comments made by Prime Minister Prayut Chan-o-cha.
The attacks came just days after voters approved a new draft constitution in a referendum, which Gen Prayut and others have said would bring greater stability to the country.
However, police have not concluded whether the incidents were motivated by the referendum outcome or political conflicts, Pol Maj Gen Piyaphan said.
Authorities are also looking into whether fires in Nakhon Si Thammarat and Surat Thani were linked to the blasts or not.
So far, "some suspects" have been detained for questioning, said Pol Maj Gen Piyaphan. He declined to say how many were being held.
But local TV stations reported that two men were being questioned for suspected involvement in the explosions.
National police chief Chakthip Chaijinda on Friday ordered all police agencies to tighten security at important government offices and symbolic places, particularly bus terminals, railway stations, airports, tourist attractions and areas frequented by tourists in the wake of the explosions.