Singapore hanged three people for drug offences last week, bringing the total number of executions to 17 this year - the highest since 2003,
BBC reports.
These come a week before a constitutional challenge against the death penalty for drug offences is due to be heard.
Singapore has some of the world's harshest anti-drug laws, which it says are a necessary deterrent to drug crime, a major issue elsewhere in South East Asia.
Anyone convicted of trafficking - which includes selling, giving, transporting or administering - more than 15g of diamorphine, 30g of cocaine, 250g of methamphetamine and 500g of cannabis in Singapore will be handed the death sentence.
The seven activists who filed the constitutional challenge argue that Singapore's mandatory death penalty violates constitutional rights to life and to equal protection of the law.
The constitution states that "no person shall be deprived of his life or personal liberty save in accordance with law".
"Singapore's barbaric drug control regime is increasingly alone on the world stage," local activist group the Transformative Justice Collective said, noting that it is one of a few countries that continue to execute people for drugs offences.
The Singapore government maintains that removing the death penalty could lead to more dire consequences.
These include more serious crime, violence, drug-related deaths, including the deaths of innocent young children, its Home Affairs Minister K Shanmugam said earlier this year.
"As policy makers, we set aside our personal feelings, and do what is necessary to protect the majority of people.. we cannot be at peace with ourselves, if we take a step which leads to many more innocent people dying in Singapore," he wrote in a Facebook post in January.
Among those executed last Wednesday and Thursday was logistics driver Saminathan Selvaraju, who was found guilty of transporting 301.6g of diamorphine, also known as heroin, from Malaysia to Singapore on the night of 21 November 2013.
Saminathan argued that he had driven his company's trailer earlier in the day, but not when the drugs were brought into Singapore. Several drivers used the same vehicle, he said.
