Reports said three men fired two shots at the guards of the People's Democratic Reform Committee (PDRC) on Chaeng Wattana Road on Tuesday afternoon.
The guards later detained the three men, who were carrying pistols and police documents.
The officers told Luang Pu that they were assigned to gather intelligence on the protest group. The monk then called their superior to take them back to the police station and told them not to bring weapons into the rally site again, according to the reports.
Police are not supposed to be armed if mingling with the protesters.