BANGKOK — The Malaysian government began a crackdown on political opponents on Thursday, arresting three government critics, including a prominent member of Parliament, and charging a student activist with sedition.

The arrests come two and a half weeks after elections that showed the governing party, which has been in power since independence from Britain in 1957, losing support from broad portions of the electorate.

The crackdown may be an attempt to pre-empt a demonstration planned for Saturday to protest accusations of fraud in the election, analysts said.

The opposition, which is led by a former deputy prime minister, Anwar Ibrahim, won the popular vote in the May 5 election but failed to take control of Parliament because of a lopsided electoral system that gives a stronger voice to rural areas, where the governing party is strongest.