Police fanned out across Malaysia's largest city on Saturday and arrested dozens of people who tried to take par in a street protest against a law allowing detention without trial, opposition activists said.
Opposition parties were expecting thousands of demonstrators to march through Kuala Lumpur in what they hoped would be the biggest protest ever aimed at pressuring Malaysia's government to scrap the Internal Security Act, which provides for indefinite imprisonment without trial of people regarded as security threats.
Government authorities warned they would not allow the protest, saying it could undermine public peace.
Police arrested at least 69 people - most of whom were identified as protesters because they were wearing opposition T-shirts and headbands - outside the city's main mosque and other locations ahead of the planned demonstration, said Lim Kit Siang, a leader of the Democratic Action Party.
Authorities set up roadblocks across Kuala Lumpur to deter the demonstrators from trying to reach the city center, sparking massive traffic crawls. Hundreds of riot police backed by trucks mounted with water cannons stood outside train stations and shopping malls where the demonstrators had arranged to gather.
Restaurants and stores were shuttered on several streets amid concerns of possible violence. Police have often broken up previous rallies using tear gas and chemical-laced water.
The protesters planned to march to the national palace to submit a petition to Malaysia's king, the constitutional monarch, to denounce the Internal Security Act.
Human rights groups estimate at least 17 people are being held under the act, mainly for alleged links to militants and document forgery.
Human rights activists have long decried the decades-old act, instituted during the British colonial era, saying it is sometimes used to jail government critics and dampen dissent.
Prime Minister Najib Razak on Friday urged people not to join the protest. Najib has promised to consider amending the act, though government officials have repeatedly said it is necessary to safeguard national security.