Opposition activists have staged numerous peaceful demonstrations since the May 5 general elections, which the National Front coalition won with a weakened parliamentary majority. The activists insist the coalition, which has governed since 1957, retained power through bogus ballots and other irregularities, though Prime Minister Najib Razak and electoral authorities deny manipulating the results.
The latest arrests involve Tian Chua, a senior official in opposition leader Anwar Ibrahim's People's Justice Party; Haris Ibrahim, a rights activist who leads an anti-government group; and Tamrin Ghafar, an opposition party member. The men had criticised the National Front at a recent political gathering.
The Prime Minister's office issued a statement saying the men were detained "after the police received numerous reports against the defendants by members of the public."
"In such circumstances the police are required to investigate and are following due and proper process," the statement said, adding that the men would face "fair and open court proceedings" if charged.
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After his arrest, Chua tweeted that Malaysians should not allow themselves to be "overtaken by fear (but should) continue to assemble peacefully and have faith."
Sedition as defined by Malaysian law includes promoting hatred against the government.
Rights activists have long criticised Malaysia's anti-sedition law as a tool to curb democratic dissent. Najib said last year the government planned to eventually abolish the Sedition Act, which was introduced in 1949 during British colonial rule, and replace it with new laws that would strike a better balance between allowing freedom of speech and ensuring public stability.