It is believed that they worked on the planned attack for months, Prawut said, adding he is confident that some Thais were involved.
He also referred to the man in a yellow Tshirt captured by CCTV cameras and for whom an arrest warrant has been issued, saying the suspect did not use the Thai language in communicating with the motorcycle taxi driver he hired.
The police are now hunting for two men and a woman captured on the camera standing near the prime suspect for interrogation.
He is confident that the attackers are still in Thailand.