Abhisit's office said the Internal Security Act would be activated in parts of Bangkok from Nov. 28 to Dec. 14 to help keep the peace during a rally planned by the United Front of Democracy against Dictatorship, comprising mainly followers of former Prime Minister Thaksin Shinawatra, who was deposed by a 2006 military coup.

Invoking the act allows the country's internal security agency, headed by Abhisit, to order curfews and restrict freedom of movement in situations deemed harmful to national security. It also makes it easier to mobilize the military to help police.

The government routinely invokes the act ahead of rallies by the group. In April, a protest by the group in Bangkok turned violent, and the army had to use force to restore order.

The planned protest is part of an ongoing political war between supporters and opponents of Thaksin that has destabilized Thailand for more than three years. Thaksin's critics accused him of corruption and disrespect to the country's revered constitutional monarch, King Bhumibol Adulyadej.

But his supporters deny disrespect to the king and point out that Thaksin won two landslide election victories and initiated social welfare programs that benefited the country's poor rural majority when he was prime minister in 2001-2006. They charge that the country's ruling elite conspired to destroy democracy to oust Thaksin and install Abhisit.

The government is also considering applying the security act on Sunday in the northern city of Chiang Mai during a scheduled visit by Abhisit, who is supposed to give a speech there to the Thai Chamber of Commerce.

The city is a stronghold of Thaksin supporters, and a leader of a sometimes violent faction of his partisans has reportedly threatened on radio broadcasts to cause harm to the prime minister.

Thaksin, a former telecommunications billionaire, fled Thailand last year to escape a conflict of interest conviction and a two-year prison sentence.

His political battle with the Thai government has prolonged a bitter division among Thais. He retains huge popularity among his rural poor power base, but is reviled by many in the educated urban elite, who led months of street protests against him.