By Ambika Ahuja

BANGKOK - Thailand passed a tough security law on Tuesday, giving the military broad powers to control a street rally that begins this weekend by supporters of exiled former premier Thaksin Shinawatra.

The Internal Security Act (ISA) allows troops to impose curfews, operate checkpoints, restrict movements of protesters and act fast if rallies by the United Front for Democracy against Dictatorship (UDD) turn violent.

Deputy government spokesman Supachai Jaisamut said the Thai cabinet approved the use of the ISA from November 28 to December 14 in Bangkok, where anti-government protesters plan to rally.

Thaksin's red-shirted supporters plan to gather on Saturday in the historic heart of the capital before marching to an intersection near Prime Minister Abhisit Vejjajiva's office on November 29, pressing demands for fresh elections.

The group has said it will then march on key roads in Bangkok on November 30 before peacefully dispersing on December 2 as the country begins celebrations for the birthday of revered King Bhumibol Adulyadej, Thailand's sole unifying figure.

"We have to make sure we can keep peace and order," Supachai told reporters. "We are concerned they may spread out and go on different routes across town which may lead to chaos, so the government invoked the law that covers the whole city."

Protesters brought traffic in Bangkok to a standstill for several days in April, occuping major intersections and sparking Thailand's worst political violence in 17 years.

Protesters hijacked petrol tankers, torched dozens of public buses and hurled petrol bombs at troops. Two people were killed.

Since April, the group has rallied briefly and peacefully in Bangkok under the special security law on six occasions.

After two unprecedented landslide election victories, Thaksin was ousted in a military coup in 2006 and now lives in exile after fleeing ahead of a two-year prison sentence for graft.

Security concerns have also been raised by Abhisit's plan to visit the northern region of Chiang Mai, Thaksin's hometown, for a business meeting on Sunday.

Some cabinet members and army officials say it could lead to protests, especially after an indirect threat on his life by one of the province's protest leaders on a community radio station.

Thaksin remains widely popular among the rural and urban poor who benefited from his populist policies but is deeply reviled by Bangkok-based power clique of the palace circle, the military, bureaucracy and the middle-class.