"Some senior officers are trying to coerce witnesses to give statements accusing the PAD of posing a security threat by organising street protests," said PAD spokesman Suriyasai Katasila, adding that these police officers had dropped hints about arresting witnesses and their relatives if they refused to cooperate.

The list of witnesses includes social critic Sulak Sivarak, activist Pitaya Wongkul, labour leader Wilaiwan Sae Tia and student leader Kochawan Chaiyabutr.

PAD leader Somkiart Pongpaiboon said he and four colleagues would not report to the police for questioning and reserved their right to testify in court.

Police are acting suspiciously in trying to charge PAD leaders with treason even though public prosecutors have refused to file such charges citing weak evidence, Somkiart said.