The Court of Appeal had said on Friday it found no merit in the appeal by a lawyer representing Kho Jabing, 31, that challenged the constitutionality of the death penalty in Singapore.

It left the timing of the execution to prison authorities.

Rachel Zheng of the Singapore Anti-Death Penalty Campaign says she was informed by Kho's family that he was executed at 3.30 p.m. Friday.

Kho was on death row for the murder of a construction worker in 2008.

Singapore's highest court on Friday rejected an appeal by a Malaysian murder convict, leaving him no further room for reprieve from execution.

The Court of Appeal said it found no merit in the last-minute appeal by an activist lawyer representing Kho Jabing that challenged the constitutional legality of the death penalty in the city-state. The rejection concludes six years of legal twists during which Kho, 31, was sentenced to death, won appeals, resentenced to life imprisonment and caning, and again sentenced to death.

No date was set for the execution, and the court said it will leave it to prison authorities to carry it out. Executions in Singapore are by hanging, and are usually carried out before dawn at Changi prison. He was supposed to have been hanged Friday, but won a last-minute reprieve late Thursday, when the Supreme Court allowed lawyer Jeannette Aruldoss Chong, to file an appeal on the constitutional grounds.

Kho is accused of using a tree branch to assault and rob a construction worker in 2008. The worker died from multiple skull fractures and Kho was convicted and sentenced to death in 2010.

Delivering the judgment, Court of Appeal Judge Chao Hick Tin said that the court's processes have been abused.

"This case has been about many things. Today, it is about the abuse of the process of the court."

Chong had "used the civil jurisdiction of the court to mount a collateral attack" on previous decisions. "If allowed... (this) would throw the whole system of justice into disrepute," he said. "No real issue of any merit had been raised" and the appeal was "plainly misconceived and bound to fail," Chao added. "Accordingly, we dismiss this appeal."

Kho clapsed his hands together as the sentence was delivered and looked down. His mother, sister and aunties were present in court and broke down after being allowed to speak to him. 

The European Union and Amnesty International have called on Singapore to grant Kho clemency.

According to the prison records, Singapore carried out four executions in 2015, one for murder and three for drug crimes. In 2012, Singapore amended its laws on the death penalty, making it no longer mandatory for those convicted of drug trafficking or murder to face the gallows.