The Metropolitan Police Bureau (MPB) will deploy at least 5,700 officers to ensure public order and security during Saturday's anti-government rally in the capital.
Pol Maj Gen Piya Tawichai, deputy commissioner and spokesman of the MPB, said the bureau has ordered 35 companies of 150 police officers on standby for the demonstration with 14 checkpoints set up around the protest venue.
He said three protest groups have announced they will take part in the rally.
The Free Youth group will gather at Democracy Monument on Ratchadamnoen Avenue before they march to the Grand Palace.
The Archeewa Pithak Prachachon Pua Prachathipatai (Vocational Students for Democracy) will hold a car mob rally at Phan Fa Lilat Bridge and move to Government House.
The Daeng Kao Na 63 (Progressive Red) will converge in their respective provinces before moving to the Democracy Monument.
Pol Maj Gen Piya said that intelligence reports suggest a possible violent confrontation as some demonstrators are known to create disturbances.
Citing the national police chief, the MPB deputy commissioner said protest leaders or activists who have outstanding warrants will be detained.
"If there are attempts to break in or set fire to property or use petrol bombs, police are told to intervene so the situation will not get out of control. Those facing arrest warrants will be taken into custody," he said.
Pol Maj Gen Jirasan Kaewsaengek, MPB deputy commissioner in charge of traffic, on Friday urged motorists to avoid all routes near Democracy Monument, Sanam Luang and Government House. At least 13 routes are likely to be affecte, he said.
Meanwhile, a protest group from Samut Prakan led by former Pheu Thai MP Worachai Hema is widely expected to opt out of today's demonstration.
Mr Worachai, also a core member of the red-shirt United Front for Democracy against Dictatorship, announced early this week that a car mob from Samut Prakan would join the rally to demand the ouster of Prime Minister Prayut Chan-o-cha.
He said yesterday the group planned to join the "car mob" rally by former red-shirt leader Nattawut Saikuar, but just learned that Mr Nattawut would not take part in today's protest.
"If there is just one car mob rally from Samut Prakan, it won't be powerful. We want to see car mob rallies from several places to take place simultaneously in a show of force," Mr Worachai said.
Preeda Kongpaen, Asst Prof Suchart Setthamalinee, Sayamol Kraiyoonwong and Wasan Paileeklee, four members of the National Human Rights Commission, will monitor today's demonstrations, according to an NHRC, adding they will observe if the people's freedom of expression is protected and if they are peaceful.