Invoking the Internal Security Act (ISA) to pre-empt possible violence during the upcoming anti-government red-shirt rally in Thailand remains an option for the government, top security officials said on Friday (March 5).

Thailand's anti-government red-shirt protesters are planning to bring in more than 60,000 people and 35,000 pick-up vans to Bangkok next week to oust the government. These demonstrations are expected to "shut Bangkok down".

A meeting of the Security Situation Monitoring Committee will be held on Monday, during which the need to impose the ISA will be reviewed.

The government has declined to comment on the necessity of invoking the ISA, but recent developments, including open threats of violence by pro-Thaksin hardliners, have caused considerable anxiety among the public.

"If we conclude there is a high chance of violence, we may propose the Cabinet invoke the ISA," said General Pirun Paewpolsong, Army chief of staff and secretary-general of the Internal Security Operations Command.

The ISA authorises the government to deploy troops to control potentially explosive situations, restrict the public's movements and regulate the media.

The committee is concerned about possible acts of sabotage aimed at creating chaos, he said, adding that security units were already prepared and on alert.

Army chief General Anupong Paochinda said Deputy Prime Minister Suthep Thaugsuban, who is in charge of national security, would have the final say on whether to invoke the ISA.

"There are many considerations, such as the possible effect on Thailand's image and the economy," he said.

Meanwhile, General Chavalit Yongchaiyudh, chairman of the opposition Pheu Thai Party, cautioned any talk about violence would only hurt Thailand's image.

"If you ask me, the government should not jump to the conclusion that the ISA is needed. But the government must do what it must do. Just don't go around advertising it. The more you talk, the more the whole world knows about it," Chavalit said.

However, protest organiser and red-shirt leader Natthawut Saikua Friday pledged an orderly and peaceful protest and dismissed fears of violence.

"We've mapped out a detailed plan, and our protests will intensify day by day in order to achieve our objective of forcing a House dissolution," he said.

"Thai citizens must decide to shut down Bangkok for a few days if the country is to move forward."

Natthawut said the crowds would be well behaved but relentless in pushing for the collapse of the government. The red shirts do not condone violence as alleged by the authorities.

He said the planned rally would project an impressive show of force and that the prime minister would see for himself the strength of the opposition before departing for an official visit to Australia.

From the main rally site in Sanam Luang, the crowds will surge into Rajdamnoen Avenue, passing the main rally stage at the Phan Fah Bridge on their way to the Royal Plaza, Natthawut said.

The red shirts will install loudspeakers on both sides of the avenue to enable the protesters to follow the speeches from the stages. Guard posts, first-aid tents and food- and water-distribution centres will be set up at designated locations throughout the rally site.

The plan is to confine the rally to the main site, but the red shirts will announce in advance if they decide to hold mini-rallies at other locations.

A week before the mass rally starts, the red shirts have already notified organisers they will bring at least 35,000 pickups to the rally site.

They have also threatened to seize any tow trucks the authorities use to try to remove the vehicles from the streets.

The red-shirt faction, led by Natthawut, Jatuporn Promphan and Veera Musigapong, insists it is not linked to the violence-prone clique of Maj-General Khattiya "Seh Daeng" Sawasdipol and Panlop Pinmanee.

It does admit to an alliance with the Pheu Thai Party but says it maintains an independent leadership.