The government had earlier declared Silom Road, a thoroughfare studded with banks and office buildings, off-limits to the protesters who have camped in the capital's main shopping district nearby for weeks.
Soldiers also patrolled the city's most famous bar strip, Patpong Road, and an entertainment area for Japanese tourists, which are just off Silom. Some took positions atop buildings after searching for possible snipers.
As Thailand's traditional New Year holiday ended, protest leaders had called for a mass rally Tuesday on Silom in their bid to oust Prime Minister Abhisit Vejjajiva. That has raised concerns of more clashes after savage fighting a week ago killed 25 people.
The military declared the city's main shopping boulevard unsafe Sunday because of large crowds of anti-government protesters, and soldiers were sent to nearby high-rises to watch for any violence.
The warning by army spokesman Col. Sansern Kaewkamnerd was another blow for Thailand's vital tourism sector, which accounts for 6 percent of the economy and has steeply declined since the protests began March 12.
Sansern said military checkpoints were being set up at entry points to the capital and within Bangkok to try to prevent more “Red Shirt” protesters from reaching the main rally site. The area contains upscale shopping malls and five-star hotels that have been under virtual siege. At least six malls remain closed.
“The protest area is unsafe. Authorities need to control it by sending security personnel into the surrounding high-rise buildings,” Sansern told a news conference. He said soldiers would help “prevent people with ill intentions from infiltrating the area.” The government accuses “terrorists” armed with guns and other weapons of orchestrating the earlier violence and says weapons were stolen from the military that have not been returned.
The protesters consist mainly of poor rural supporters of former Prime Minister Thaksin Shinawatra and pro-democracy activists who opposed the military coup that ousted him in 2006.
They believe Abhisit heads an illegitimate government because it came to power through a parliamentary vote after disputed court rulings ousted two elected, pro-Thaksin administrations. The conflict has been characterized by some as class warfare, pitting the country's vast rural poor against an elite that has traditionally held power.
Meanwhile, the rival, establishment-backed “Yellow Shirt” protest movement vowed Sunday to take action unless the government “strictly and efficiently enforces the law” to deal with the crisis.
The yellow-shirted protesters led months of anti-Thaksin rallies that led to the coup and their 2008 demonstrations shut Bangkok's airports for a week to protest a Thaksin-allied government. They retreated after Abhisit's arrival but many fear their return if he is forced out.
Abhisit has come under increasing criticism for failing to clear the protesters, but the government spokesman said Saturday there were no immediate plans for a crackdown because too many people were camped in the area to use force.
Sansern, however, said the army would not allow protesters to march to another location and would not tolerate more violence.
“We will not allow people to hurt police officers, soldiers or civilians again - or to seize military vehicles or weapons,” he said.
The Red Shirt protesters, formally known as the United Front for Democracy against Dictatorship, want Abhisit to dissolve Parliament and call new elections. They were initially camped in a historic district of Bangkok, and a failed attempt by security forces on April 10 to flush protesters from that neighborhood erupted into the worst political violence Thailand has seen in 18 years.
At least 25 people were killed, including senior military officers. More than 800 people were wounded, including about 300 soldiers.
Since then, the protesters have consolidated in Bangkok's main shopping area, raising the stakes as they scare off tourists and rattle the stock market. Retailers and hotels say they have lost tens of millions of dollars.
Portable toilets and tents have been trucked in, and vendors line the streets selling food, sleeping mats, clothing and red-colored souvenirs such as T-shirts, headbands and baseball caps.
“The authorities have always tried to block people from joining us. But still we are getting more people,” said one protest leader, Jatuporn Prompan, on Sunday.
Police have issued 24 arrest warrants for Red Shirt leaders accused of inciting violence, but so far none has been arrested. An attempt to arrest one leader Thursday was thwarted when he climbed over a hotel balcony and was lowered by rope to a crowd of fellow Red Shirts, who helped him escape.
