A Singapore rights lawyer, one of a handful defending death-row convicts in the city-state, was suspended for five years on Tuesday for making "baseless" allegations against the judicial system.

M. Ravi had told an online publication outside the Supreme Court in 2020 that the public prosecutor had been "overzealous in his prosecution", after he helped a Malaysian drug convict escape the death penalty on review.

While Singapore is economically successful and ranks among the world's least corrupt countries, rights groups frequently accuse the government of restricting free speech and civil liberties.

"No solicitor can be permitted to recklessly and baselessly undermine the very pillars of the legal system in which he... operates; to do so would plainly cause grave injury to public confidence in the legal profession," the court said in its decision.

"In our judgment, Mr Ravi's misconduct exhibits a fundamental lack of respect and a blatant disregard for the integrity of Singapore's key legal institutions," it added.

After winning the 2020 review for Gobi Avedian, the outspoken lawyer had also asked the state, the prosecutors and the law minister to apologise to his client.

He made further allegations of improper conduct by prosecutors, and threatened to sue the Law Society of Singapore if it did not protect the independence of lawyers or if it participated in any "harassment" by the attorney general against him.

Ravi was also suspended for a year in 2007 for being disrespectful to a judge.

In a Facebook post Tuesday, Ravi said he was just happy he had been able to save Gobi from the gallows and was leaving the decision against him "to the court of public opinion".

Human Rights Watch deputy Asia director Phil Robertson condemned Ravi's suspension.

"In democracies around the world, it is expected that lawyers will speak their minds about the outcome of a trial they've been involved in but Singapore punishes such expression, and their society is poorer for it," he said.

One of Ravi's numerous death-row clients was Malaysian national Nagaenthran K. Dharmalingam, who was executed for a drug offence last year despite being mentally disabled.

The case drew international protests, including from British tycoon Richard Branson.