Defending the decision to invoke a draconian security law against ethnic-Indian leaders, Malaysian premier Abdullah Badawi has said their actions "could be deemed as treachery" while an opposition party announced it will challenge the move in court.

Abdullah said Hindraf's allegations of "ethnic cleansing" and marginalisation of ethnic-Indians in Malaysia had hurt the country's image and could seriously impair efforts to attract investors and tourists.

"These actions could be deemed as treachery," he was quoted as saying by media here after signing the detention orders for five Hindu Rights Action Force (Hindraf) leaders under the Internal Security Act (ISA) which allows detention without trial.

"Yes, I have signed the detention orders and there is nothing more to explain," Abdullah said.

"When I feel the situation warrants it, I just sign," he said after a close-door meeting with Brisan leaders, declining to reveal if more people would be detained.

 However, the police said "others involved or having links with any terrorist organisation that could threaten or jeopardise national security will be picked up".

Abdullah said the country's peace and security superseded the freedom of speech. "I value what is freedom, but law and order is more important and needs to be preserved," he said.

The opposition party DAP said it will file a habeas corpus application to challenge the order detaining five Hindraf leaders under ISA.