Singapore on Wednesday executed a man convicted of drug trafficking, a representative for his family said, despite pleas from his relatives and activists for clemency.

Tangaraju Suppiah, 46, had been convicted for abetting the trafficking in 2013 of more than 1 kg (2.2 pounds) of cannabis, double the threshold for the death penalty in the city-state, which is known for its tough laws on narcotics.

Kokila Annamalai, a Singapore-based rights activist representing the family, confirmed Suppiah had been executed by hanging after the president had rejected pleas for clemency on the eve of the execution.

The Singapore government did not immediately respond to a request for comment.

British billionaire Richard Branson, a well known opponent of the death penalty, had said the verdict against Suppiah did not meet standards for criminal conviction as he was not near the drugs when he was arrested.

The government in response said Branson was peddling falsehoods and disrespecting its justice system, adding that its courts spent more than three years examining the case and Branson's claim was "patently untrue".

The United Nations Office for Human Rights had also called for Singapore not to proceed with the execution and to "adopt a formal moratorium on executions for drug-related offences".

Singapore executed 11 people last year and says the death penalty is an effective deterrent against drugs and that most of its people support the policy.