Police have arrested a Malaysian opposition lawmaker and two journalists under a law that can keep them detained indefinitely without trial, sparking fears of a major government crackdown on dissent at a time the opposition is trying to seize power.

Opposition parties denounced Friday’s arrests as a violation of human rights and a setback to democracy.

Online commentator Raja Petra Raja Kamarudin, who is a well-known anti-government activist, was the first to be detained under the Internal Security Act, a widely criticized law that provides for the arrest of those suspected of threatening national security. His wife Marina Lee Abdullah said police picked him up at their home.

Hours later, police arrested Tan Chee Hoon, a reporter with Chinese-language daily Sin Chew, in northern Penang state after earlier warning her paper that it could be shut down for its coverage of sensitive issues. Opposition lawmaker Teresa Kok was the third to be detained near her home in a Kuala Lumpur suburb.

Police gave no reason for any of the arrests, which come as Prime Minister Abdullah Ahmad Badawi faces renewed pressure from his ruling party to resign. Tensions have also risen amid a threat by opposition leader Anwar Ibrahim to topple the government by Tuesday.

“Invoking the ISA just days before September 16 is clearly an attempt to engineer an atmosphere of fear and instability,” Anwar said in a statement.

“By sanctioning the use of the ISA to avert the process of transformational change in Malaysia, the … government is confirming that it has lost touch with the will of the people,” he said.

Lim Guan Eng, secretary-general of the another opposition party, the Democratic Action Party, called the arrests “a travesty of justice.”

“It’s a desperate act to cling on to power,” said Lim.

The developments underscored the increasing sense of political insecurity in a country that has long been considered one of Southeast Asia’s most stable territories.

Raja Petra has infuriated authorities by publishing numerous claims about alleged misdeeds by government leaders on his Web site, Malaysia Today. The government has denounced many of Raja Petra’s accusations as lies. He was charged with sedition in May for allegedly implying the deputy prime minister was involved in the killing of a young Mongolian woman.

The arrests come just a day after authorities lifted a two-week ban on Malaysia Today. The ban sparked a public outcry, with many accusing the government of censoring cyberspace.

Though it lifted the ban, the government has warned it will use the Internal Security Act against anyone who stokes political and racial strife.

Sin Chew reporter Tan reported comments by a Malay Muslim ruling party politician last month who described ethnic Chinese minority as “squatters” and accused them of hungering for power. The remarks sparked outrage nationwide, and the politician was suspended by Abdullah’s party.

Lawmaker Kok has allegedly complained about the noise of morning prayers from a mosque in her electorate.

Abdullah has promised to hand power to his deputy, Najib Razak, in mid-2010 but he is battling growing demands from dissidents in his own party to resign earlier.

His National Front coalition lost its two-thirds parliamentary majority in March elections. Anwar has said he will oust the government with parliamentary defections this month. He needs at least 30 government lawmakers on his side to take over.