The latest attack was early Tuesday morning when a grenade landed at Gate 4 of Lumpini Park. One injured man was taken to hospital and two others reported slightly injured.
Mr Thaworn said the joint security system would help end the accusation that attacks were being perpetrated by PDRC guards. The checkpoints around the park are currently jointly manned by the police and the army.
He questioned the actions of Lumpini police prior to the attack on Thursday night. He said police had asked prostitutes working around the park to leave the area 15 minutes before shots were fired at a taxi. The driver claimed protest guards open fire on his car while he had a customer cruising looking for a prostitute.
Mr Thaworn said the protesters had discover the taxi belongs to a police officer at Nang Lerng police station and it was driven by a policeman from that station to Rama 4 Road.
He said when the taxi was being fired at Lumpini police station also switched off the lights. Mr Thaworn was later told that the lights were doused so police would not be targeted. However, the PDRC tended to believe that Lumpini police station knew beforehand about the shooting.
It has been suggested the "passenger" in the taxi opened fire first.
Meanwhile, PDRC guards have been instructed to tighten security and nets have been strung up at the back of the main stage, to block any grenades, as that is considered a risk area for possible attack.