The materials can be bought anywhere. But it's the people that you have to investigate to see if there are connections," he said.
Pol Gen Chakthip said police have sought help from Malaysian authorities because the type of mobile phones used in the bomb blasts was sold in Malaysia only and it is possible the suspects might have fled there.
Prime Minister Prayut Chan-o-cha said authorities are still investigating the attacks and the government is not accusing any individual or groups of being behind the violence.