Malaysian Prime Minister Najib Razak has introduced new legislation that would prevent police from indefinitely detaining suspects without trial or arresting people for their political beliefs.

The bill presented Tuesday to the lower house of parliament would replace the notorious Internal Security Act, a draconian, 52-year-old law that has long been used to hold opposition leaders and other government critics without trial.

Under the new law, police can detain those suspected of terrorism or deemed a security threat for up to 28 days without pressing charges. It also says no one can be arrested or detained “on the basis of their political affiliation, activity, or belief.”

In a statement Tuesday, Mr. Najib hailed the law as “another major step forward on the road to reform.” The prime minister has promised a series of political reforms ahead of national elections that are expected to be called with a few months.

Opposition leaders and activists welcomed the proposed changes. But some say Mr. Najib is forced to make the reforms because his National Front party is struggling to maintain its majority in parliament.

Malaysia's opposition parties have been gaining support ahead of the expected elections by demanding improved human rights guarantees and greater transparency in government.

The new security bill is expected to be approved by lawmakers and endorsed by Malaysia's constitutional monarch in the coming weeks.