GENEVA (Reuters) - United Nations human rights experts called on Iran to spare the life of a man, due to be executed on Thursday, who was convicted of raping and killing a child when he was a juvenile.

Amirhossein Pourjafar, who was 16 when he was sentenced to death in September 2016, a year after the crime, is among more than 80 youths known to be on death row in the Islamic Republic.

Pourjafar, believed to be held at a prison in the city of Karaj, was already scheduled to be executed in October 2017 when the experts made a previous 11th-hour appeal. He turned 18 last month according to the Western calendar, a U.N. official said.

“He is due to be executed on Thursday 4 January in direct contravention of international standards on the use of the death penalty”, said Asma Jahangir, U.N. special rapporteur on human rights in Iran, and Agnes Callamard, U.N. special rapporteur on extrajudicial, summary or arbitrary executions.

“The Iranian authorities must immediately halt the execution of this juvenile offender and annul the death sentence against him in compliance with their international obligations,” they said in a joint statement.

Iran has signed an international treaty strictly banning the execution of people who commit crimes under the age of 18.