Security is tight in Bangkok as Thaksin Shinawatra's supporters plan to hold a mass rally to mark the third anniversary of the coup that ousted their leader as Thailand's prime minister.
The government has imposed the Internal Security Act around the rally venue.
From early morning on Saturday, military checkpoints had been set up as well as barricades to contain any potential violence.
Thousands of police and military personnel in anti-riot gear secured the area.
The government has invoked the Internal Security Act until September 22, allowing the military to close roads and make arrests.
Members of the United Front for Democracy Against Dictatorship, who wear red shirts to distinguish themselves, plan to gather at the Royal Plaza before marching to the residence of the king's adviser, Prem Tinsulanonda, in the afternoon.
King Bhumibol Adulyadej, 81, has reigned for more than six decades, serving as head of state through 15 successful or attempted coups and 16 constitutions.
Thai police deployed about 600 police to protect Prem's house in the country's northeast, where he planned to stay during the pro-Thaksin rally, the Bangkok Post reported on Friday, without citing where it got the information.
Panitan Wattanayagorn, a spokesman for the Thai government, told Al Jazeera: "Demonstrations in a democratic society is normal as long as there is order, are held under the law and there is no violence."
Violent street protests by Thaksin's supporters and opponents have blocked roads, airports and government buildings, bringing Bangkok to a halt twice in the past year.
Thaksin won landslide election victories in 2001 and 2005 but was overthrown in the coup.
But he was convicted last year by the supreme court's Criminal Division for Holders of Political Positions on conflict of interest charges in relation to a land purchase scandal.
Earlier in the year, hundreds of Red Shirt protesters stormed an Association of Southeast Asian Nations (Asean) meeting in the beach resort Pattaya.
The protest spread to Bangkok where troops were called in to bring Thaksin supporters under control and to remove them from Government House which they had been occupying for months.
Royal pardon plea
In August, Thaksin supporters submitted a petition, requesting a royal pardon for the fugitive politicians including Thaksin and his former party members, but a pardon has not been granted.
Thaksin remains popular among Thailand's rural poor for the populist policies he introduced.
|Shinawatra remains popular among Thailand's rural poor despite his self-imposed exile [EPA]
Despite being in self-imposed exile, Thaksin remains an influential force and has sent almost daily video and audio messages to Red Shirt rallies, supporting their call for the current prime minister to resign and hold fresh elections.
The Red Shirts took their cue from protests last year by rival Yellow Shirts, who took to the streets in huge demonstrations against successive pro-Thaksin governments.
Those protests culminated in the shutdown of Bangkok's two airports and court rulings ordering the dissolution of the government, paving the way for Abhisit Vejjajiva to become prime minister in December.
The Red Shirts took to the streets again last month, accusing Abhisit of taking power illegally.
They say the Thai elite - the military, judiciary and other unelected officials - are interfering in politics, and are seeking Thaksin's rehabilitation.