Police have warned anti-government protesters at Wednesday's rally in Bangkok to stay at least 150 metres away from the Crown Property Bureau (CPB).
A Bangkok police source said 6,000 policemen had been assigned to handle Wednesday's protest and he vowed that they would enforce the law against all offenders.
Pol Maj Gen Piya Tawichai, deputy chief of the Metropolitan Police Bureau (MPB), said on Tuesday that demonstrators must not enter within a 150-metre radius of the premises under the public assembly law.
The MPB has prepared crowd control units and set up security checkpoints to handle the demonstrators. It will also cordon off the streets leading to the CPB, Pol Maj Gen Piya said.
If protesters breach the cordon, police would take measures to stop them, he said, pointing out that officers are duty-bound to uphold the law.
Deputy Prime Minister Prawit Wongsuwon said on Tuesday that the CPB was off-limits to protesters but also warned against any efforts to hold a counter-demonstration against the planned anti-government rally.
Gen Prawit said the authorities would ensure there was no confrontation between the two rival groups and that he had instructed police to keep an eye on so-called "third-party" activists who might try to instigate violence.
A source said Gen Prawit and representatives of the security agencies on Tuesday attended a war room set up at the Five Provinces Bordering Forests Preservation Foundation on Vibhavadi Rangsit Road to monitor the activities of the anti-government group.
Pol Col Kissana Phathanacharoen, deputy spokesman of the Royal Thai Police, said that the protest movement led by Ratsadon (People's Movement) and the Free Youth group had not sought police permission to hold Wednesday's rally.
He said that while the right to hold rallies was guaranteed by the constitution, demonstrators must adhere to the public assembly law by asking for police approval at least 24 hours in advance. Their rallies must also be peaceful and not infringe on others' rights, he said.
Army chief Gen Narongphan Jittkaewtae said that police would be the main enforcer of the law on Wednesday but that soldiers would also be on hand to assist them if required.
The pro-democracy Free Youth group on Tuesday asked supporters to first meet at 3pm at Democracy Monument on Ratchadamnoen Avenue before moving on to the nearby CPB in Nakhon Ratchasima Road to "reclaim assets that should have belonged to people".
Thanu Kwandet, acting deputy permanent secretary for the Education Ministry, has told staff to work from home on Wednesday to avoid the rally, since the ministry is near the CPB, the demonstrators' main target.
Saint Gabriel's College on Tuesday also announced that it would be closed on Wednesday because the planned demonstration is nearby and roads around the CPB will be closed to traffic. Classes will resume tomorrow.
Two universities that are also located near the CPB -- Suan Sunandha Rajabhat University and Suan Dusit University -- also announced that they will be closed on Wednesday for the safety of staff and students.
Former Democrat Party MP Warong Dechkitvigrom, now leader of the pro-monarchy Thai Pakdee (Loyal Thais) group, on Tuesday asked supporters not to go to the CPB and to thereby avoid confrontation with anti-government protesters.
Another royalist group, "The Network for the Protection of the Monarchy" will gather in front of parliament on Wednesday, although its leaders insisted they would not go anywhere near the CPB.
A new group, Siam Land, also announced on Tuesday it would go the CPB on Wednesday and vowed to stop the Free Youth protesters from going there, although it pledged there would be no violence.
Progressive Movement leader Thanathorn Juangroongruangkit on Tuesday asked police and the government to hear what protesters had to say, explaining that those demonstrating on Wednesday were doing so because their demands were being ignored.