Nagaenthran Dharmalingam, 34, had been on death row for over a decade after he was convicted of trafficking about 43 grams of heroin into Singapore.
A Malaysian man convicted of drug trafficking has been executed in Singapore despite appeals for clemency on the grounds that he had an intellectual disability, his family said.
Nagaenthran Dharmalingam, 34, had been on death row for more than a decade for trafficking 44 grams of heroin into Singapore, which has some of the world's toughest narcotics laws. His lawyers had filed multiple appeals against his execution saying he was intellectually disabled.
His brother Navin Kumar, 22, said by telephone the execution had been carried out on Wednesday and said the body would be sent back to Malaysia where a funeral would be held in the town of Ipoh.
The 34-year-old was executed in the early hours, his sister Sarmila Dharmalingam told the AFP news agency.
"It is unbelievable that Singapore proceeded with the execution despite international appeals to spare his life," she said, speaking from Malaysia.
She added the family was "extremely saddened" and "in a state of shock".
"On this score may I declare that Malaysia is far more humane. Zero to Singapore on this."
A Singapore court on Tuesday had turned down a legal challenge put forward by Nagaenthran's mother, clearing the way for the execution by hanging.
At the end of Tuesday's hearing, Dharmalingam and his family reached through a gap in a glass screen to grasp each others' hands tightly as they wept. His cries of "ma" could be heard around the courtroom.
About 300 people held a candlelight vigil at a Singapore park on Monday to protest against the planned hanging.
Nagaenthran's case has attracted world attention, with a group of United Nations experts and British billionaire Richard Branson joining Malaysia's prime minister and human rights activists to urge Singapore to commute his death sentence.§
His lawyers and activists have said Nagaenthran's IQ was found to be at 69, a level recognised as an intellectual disability. However, the courts determined he knew what he was doing at the time of his crime, and ruled there was no admissible evidence showing any decline in his mental condition.
'Tragic miscarriage of justice'
Reprieve, a nonprofit organisation of international lawyers and investigators called the execution of Nagaenthran a "tragic miscarriage of justice."
"Nagen's execution is a flagrant violation of international laws that Singapore chose to sign up to. From rushed hearings to intimidation of Nagen’s lawyers, this case has laid bare Singaporean authorities’ hollow claims about affording due process," Reprieve said.
"His last days were spent, like much of the last decade in torturous isolation of solitary confinement. He had to get the court’s permission to hold his family’s hands yesterday. Our thoughts are with his family, who never stopped fighting for him; their pain is unimaginable."
The Singapore government says the death penalty is a deterrent against drug trafficking and most of its citizens support capital punishment.