SINGAPORE: A lawyer for a Malaysian man sentenced to hang for smuggling heroin into Singapore asked judges for mercy during his appeal on Tuesday, and urged more time to seek further psychiatric assessment to prove his mental impairment.

Nagaenthran Dharmalingam has been on death row for more than a decade for trafficking 42 grammes (1.48 oz) of heroin into Singapore, which has some of the world's toughest narcotics laws. He has appealed on the grounds of mental disability.

His lawyer Violet Netto asked for "mercy" from the judges in allowing time to arrange an independent psychiatric evaluation.

The Court of Appeal was expected to make a decision on Tuesday but reserved judgement until an undisclosed date.

Nagaenthran's case has attracted international attention, with Malaysia's prime minister, a group of United Nations experts and British billionaire Richard Branson joining human rights groups in urging Singapore to commute his death sentence.

Singapore hanged 25 people from 2016 to 2019, according to official data, mostly for drug-related crimes.

During Tuesday's proceedings, Chief Justice Sundaresh Menon said Nagaenthran's lawyer was abusing the court process by submitting reports late and that her actions appeared "calculated to delay".

Menon said Netto had prevented the disclosure of her client's prison medical records, which would have helped the judges reach a decision on the appeal.

The lawyer had objected to presenting the records, which included a psychiatric assessment, citing patient confidentiality.

Nagaenthran's defence and human rights groups have argued that his intellect was at a level recognised as a mental disability and say he has other disorders affecting decision-making and impulse control.

The court stayed his execution last year without ruling on his appeal after he tested positive for COVID-19 a day before he was due to be hanged.

Nagaenthran's sister, Sarmila Dharmalingam, on Tuesday said she would keep praying for her brother's life.

"Many thanks to each and every one who putting effort to save my brother's life. Keep on praying," she said.