
Some 600 police will be stationed at Sanam Luang, the planned venue for the rally, according to Metropolitan Police commissioner Lt-General Worapong Chiewpreecha.
He expressed confidence that police would be able to deal with the anti-government mob, who were expected to gather in "large numbers", according to police intelligence.
The city police chief said the protesters would not be allowed to seize Government House and would be arrested if they tried to do so.
A police source said regional police bureaux close to Bangkok and Border Police had been mobilised to provide possible reinforcements for the Metropolitan Police.