DUBAI, Aug 15 (Reuters) - Iran's parliament has taken a tentative step towards reducing the use of the death penalty for drug trafficking offences, Iranian media reported, a change which could save the lives of up to 5,000 mostly young convicts on death row.

Western human rights groups often criticise Iran for its high number of executions. Iran carried out 567 executions in 2016, mostly for drug offences, making it second only to China in its use of the death penalty, Amnesty International said.

Parliament passed a long-debated amendment on Sunday that would raise the threshold for imposing the death penalty in drug trafficking cases to 50 kg (110 lbs) of opium, and 2 kg of heroin, morphine, cocaine, or their chemical derivatives, the semi-official ISNA news agency reported.

The amended bill must still secure a second approval by parliament and then by a clerical body that vets legislation before it can become law.

Under current laws, trafficking or trading of more than 5 kg of opium or 30 grams of heroin carry the death penalty.

The more lenient arrangements would not apply to drug gangs, armed traffickers and repeat offenders, ISNA said.

Hassan Norouzi, a spokesman for parliament's judicial committee, was quoted by Iranian newspapers as saying the new law could help commute the sentences of many of the 5,000 people on death row for drug offences, the majority between the ages of 20 and 30.

The United Nations has repeatedly praised Iran's battle against narcotics trafficking but criticised its use of the death penalty.

Given Iran's large number of executions, some countries including Britain and Denmark have stopped providing funding for the United Nations drug control programme in Iran.

Most narcotics are smuggled into Iran along its long, often lawless border with Afghanistan, which supplies about 80 percent of the world's opium from which heroin is made.

(Reporting by Dubai newsroom; Editing by Gareth Jones) ((dubai.newsroom@thomsonreuters.com;))