The government will let students use part of Sanam Luang on Saturday for their political rally, a security source said on Monday.
"Intelligence believes the rally is just the first exercise for the protesters to move to Government House. Officials will negotiate with them to send representatives to lodge a petition letter at Government House instead," the source said.
The move comes despite the fact Sanam Luang ground is normally prohibited from such activities as the area is classified as a royal site.
If the students insist on moving to Government House, security officials will stop them 50 metres from building itself and 150 metres from any royal premises.
The source insisted officials would not use armed force against protesters. "These students and protesters are not enemies. Battles are engaged in with enemies only."
The source said the Saturday rally is just a "major rehearsal" before an even bigger political rally in October when the House will vote on charter amendments.
The source said protests may grow if senators vote against drafts which these student protesters supported.
"If senators veto the draft, these protesters will have a justification to escalate their movement," the source said.
Prime Minister Prayut Chan-o-cha, meanwhile, agreed the government should be prepared to let the students protest.
"The government will not do anything that will lead to violence. I have ordered officials to take care of everyone to ensure safety and make sure no one exploits this protest for their own goal," Gen Prayut said yesterday.
Second Army spokesman Maj Gen Rachan Prachantasen said there will be no military roadblocks to stop protesters from the Northeast travelling to anti-government demonstrations.
"Since the dissolution of the National Council for Peace and Order, the military is no longer responsible for maintaining law and order at various protest venues. That now lies in the hands of police and administrative officials," he said.
The military will help only when security roadblocks are needed, he said.
Some protesters from the Northeast were likely to travel to Bangkok to join the Saturday demonstration, but not in large numbers. Instead, people might hold simultaneous demonstrations in their own provinces, said Maj Gen Rachan.
A police source said Pol Maj Gen Nitinan Petchabarom, deputy commander of the Metropolitan Police Bureau, said police will set up 21 checkpoints from Friday at 4pm to midnight on Saturday.