Thousands of Iranians who have been sentenced to death for drug crimes could be spared following a softening in the country's law.
Capital punishment has been abolished for some drug offences, and the head of the judiciary has said all cases on death row can be reviewed.
The move is set to be applied retroactively, meaning some 5,000 prisoners could escape execution.
Iran executes hundreds of people every year, mostly for drug offences.
In August, Iran's parliament raised the threshold on the amount of drugs that would be considered a capital offence.
Under the previous law, possessing 30g of cocaine would trigger the death penalty but that has been increased to 2kg (4.4lb). The limit on opium and marijuana has been increased tenfold to 50kg.
Judiciary chief Ayatollah Sadegh Larijani told local media that most death sentences would be reduced to extended jail terms.
Mahmood Amiry-Moghaddam, from Iran Human Rights (IHR), an independent NGO based in Norway, welcomed the law change.
"If implemented properly, this change in law will represent one of the most significant steps towards reduction in the use of the death penalty worldwide," he told the BBC.
But he expressed concern that those on death row might not be able to take advantage.
"Since most of those sentenced to death for drug offences belong to the most marginalised parts of Iranian society, it is not given that they have the knowledge and resources to apply for commuting their sentence," he said.
Human rights group Amnesty International also welcomed the news, but said it would like to see further progress.
"The Iranian authorities must stop using the death penalty for drug-related offences, with a view to eventually abolishing it for all crimes," a spokeswoman said.
"There are currently an estimated 5,000 people on death row for such offences across the country. About 90% of them are first-time offenders aged between 20 and 30 years old."
The group quoted an official who said that, since 1988, Iran had executed 10,000 people for drug crimes.
In 2016, Iran's then justice minister said he was looking for an "effective punishment" for criminals instead of execution. Mostafa Pourmohammadi said he thought the number of capital crimes should be revised and the death penalty kept for "corrupt people".