SINGAPORE — A court in Singapore has executed a Malaysian drug smuggler, his sister has confirmed to the BBC.

Nagaenthran Dharmalingam had been on death row for more than a decade for attempting to bring around three tablespoons of heroin into Singapore.

His case was highly controversial as he was assessed by a medical expert to have an IQ of 69 — a level that indicates an intellectual disability.

But the government said he "clearly understood the nature of his acts".

The court had earlier on Tuesday dismissed a last-ditch appeal by his mother, adding that Nagaenthran had been given "due process in accordance with the law", adding that he had "exhausted his rights of appeal and almost every other recourse under the law over some 11 years".

At the end of Tuesday's hearing, Nagaenthran and his family had reached through a gap in a glass screen to grasp each other's hands tightly as they wept, according to a Reuters report. His cries of "ma" could be heard in the courtroom.

In an earlier statement, the government said they found he "did not lose his sense of judgment of the rightness or wrongness of what he was doing".

In 2009, Nagaenthran was caught crossing into Singapore from Malaysia with 43g (1.5oz) heroin strapped to his left thigh.

Under Singapore's drug laws - which are among the toughest in the world - those caught carrying more than 15g of heroin are subject to the death penalty.

During his trial, the 34-year-old initially said he was coerced into carrying the drugs, but later said he had committed the offence because he needed money.

The court said his initial defense was "fabricated". He was eventually sentenced to death by hanging.

In 2015, he appealed to have his sentence commuted to life in prison on the basis that he suffered from an intellectual disability.

His lawyers had argued that the execution of a mentally ill person is prohibited under international human rights law.

But a court found that he was not intellectually disabled. A push for presidential clemency was also rejected last year.

"The Court of Appeal found that this was the working of a criminal mind, weighing the risks and countervailing benefits associated with the criminal conduct in question," said Singapore's Ministry of Home Affairs in an earlier statement.

The movement has gained traction on social media, where there has been an unusual outpouring of anger and sympathy, including from the British billionaire Richard Branson and actor Stephen Fry, who oppose capital punishment and have called on Singapore to spare Nagaenthran.

Thousands had also signed a petition, arguing that the execution of a mentally ill person is prohibited under international human rights law.

The execution was on Tuesday condemned by rights group Reprieve, who called him the "victim of a tragic miscarriage of justice".

"Nagen's last days were spent, like much of the last decade, in the torturous isolation of solitary confinement," said Reprieve's Director Maya Foa.

"Our thoughts are with Nagen's family, who never stopped fighting for him; their pain is unimaginable."

Singaporean anti-death penalty activist Kirsten Han also released a photo of Nagaenthran on Wednesday, which pictured him reportedly wearing his favourite outfit.

The Singapore government has argued that international law does not prohibit the death penalty and that there is no international consensus on the use of it.

They have also argued that under Singapore law, he would not have been given the death penalty if the court had found him to be "suffering from an abnormality of mind which substantially impaired his mental responsibility". — BBC