Singapore's parliament passed a law on Monday that could jail "dangerous" sex offenders and violent criminals indefinitely.

The "Sentence for Enhanced Public Protection" (SEPP) aims to keep convicts who show signs that they might re-offend behind bars, even after their jail terms have ended.

The legislation will apply to offenders convicted of serious violent or sexual offences, such as culpable homicide, rape and sex with minors.

Law and Home Affairs Minister K. Shanmugam told parliament that "with the SEPP, there can be a more calibrated approach to better protect society".

Singapore has tough laws for even minor offences, such as vandalism, which can be punished by caning.

It has a homicide rate of just 0.2 per 100,000 inhabitants, according to UN data, among the world's lowest.

Senior Parliamentary Secretary for Law Rahayu Mahzam said courts would determine whether an SEPP would be imposed on an offender.

"The court can decide not to impose SEPP if it is of the view that an ordinary imprisonment term is more appropriate," Mahzam said.

In cases where an SEPP was considered appropriate, "the possibility that the offender may be detained past the minimum period is a part of the sentence imposed by the judge", she said.

High-risk offenders would only be released if the home affairs minister assessed they no longer posed a threat to the public.

The minister would have a review board consisting of experts such as retired judges and psychiatrists, according to the SEPP law.

The law and home affairs ministries said in a joint statement last month the changes were needed because current sentencing practices "were inadequate to deal with such egregious offending".