Police yesterday searched for weapons in a tent belonging to vocational students at the Makkhawan Rangsan Bridge anti-government protest.
The protest is led by the Network of Students and People for Reform of Thailand (NSPRT).
Around 3pm yesterday, six policemen from Nang Loeng police station raided the tent, but found nothing suspicious, prompting the students to heckle and blow whistles at the officers.
The students videoed and photographed the police for evidence.
On Saturday, a policeman was assaulted, allegedly by a group of vocational students, as the students marched toward Government House during a campaign to place national flags at zones where rallies are prohibited.
Pol Snr Sgt Maj Chatri Khachonphet was attacked by five people at Nang Loeng Intersection on Phitsanulok Road. He sustained minor injuries.
The brawl was quickly stopped by key members of the NSPRT who announced through speakers: "Please do not hurt officers or you will damage our cause". The incident occurred as NSPRT members tried to enter a restricted zone to place a flag at Chamai Maruchet bridge near Government House. The group was eventually allowed to complete its mission.
Network adviser Nitithorn Lamlua said the NSPRT wanted to "awaken people to the significance of the national flag" after police reportedly vowed to act against drivers who attach flags to their cars and cause problems with traffic flow.
NSPRT members on Saturday managed to place national flags at various venues in Dusit, Phra Nakhon and Pomprap Sattruphai districts, which have been declared rally-free zones under the government's Internal Security Act.
Mr Nitithorn said yesterday the NSPRT has to check whether the men who attacked the policeman were rally participants, and what caused the brawl.
Metropolitan Police Bureau chief Kamronwit Thoopkrachang yesterday sent a letter to NSPRT co-leader Uthai Yodmanee asking the protest leaders to hold talks with police to work out security arrangements.
In the letter, Pol Lt Gen Kamronwit, who heads the Centre for the Administration of Peace and Order (Capo), said the Capo had received intelligence reports that certain ill-intentioned people might sneak into the protest venue to instigate disturbances and violence.
Therefore, the Capo will set up checkpoints around the protest site to screen people and vehicles to ensure protesters' safety.
At the Ratchadamnoen Avenue protest venue yesterday, a man aged about 50 was assaulted by guards and protesters who suspected he might be a red shirt posing as an anti-government rally participant.
The man carrying a whistle acted suspiciously near the stage and had no ID card.
When a group of 10 guards approached him, the man tried to walk away before getting into a brawl with the guards.
Ekkanat Phromphan, a former Democrat MP for Bangkok and protest spokesman at the Ratchadamnoen Avenue venue, said yesterday the government and police had voiced concerns about a "third hand". He said only plainclothes police were found to have sneaked into the protest site so far.
Deputy Democrat Party spokesman Mallika Boonmeetrakul said that police who enter any protest site must wear their ID cards.
She said some policemen were carrying weapons into the protest areas.
Without ID cards, misunderstandings and problems could ensue in the crowd, she said.
Capo spokesman Piya Uthayo said national police chief and Capo chief Adul Saengsingkaew had ordered police officers to secure government office buildings and houses of important people ahead of the Constitution Court ruling on the legality of the charter amendment draft to change the structure of the Senate on Wednesday.
Pol Maj Gen Piya said four police officers were assaulted and injured during operations to handle various groups of anti-government protesters in the period Nov 9-16. They were admitted to Police General Hospital.