Nearly 1,000 people executed in Iran in 2015

"At least 966 persons  the highest rate in over two decades were executed in 2015," Ahmed Shaheed told the UN Human Rights Council in Geneva.

In 2014, 753 people were executed.

Shaheed added that "at least 73 juvenile offenders were reportedly executed between 2005 and2015", 16 of them in the past two years alone.

"At least 160 others are awaiting the same fate on death row," he told the UN's top rights body.

In a report published in January, rights watchdog Amnesty International slammed Iran as the world's most prolific executioner of offenders convicted of committing crimes as juveniles.

The UN special rapporteur on Iran also voiced concern that in January this year, at least 47 journalists and social media activists reportedly remained detained in the country, after more than 270 Internet cafe businesses were reportedly closed in 2015 for their alleged "threat to societal norms and values".

Amnesty also accused Iran of breaking international law by failing to close a penal loophole allowing a judge to decide that girls as young as nine and boys as young as 15 bear full criminal responsibility potentially exposing them to capital punishment.

On Monday, Shaheed also addressed that issue, urging the Iranian government "to raise the age of criminal responsibility to 18 years and without discriminating between boys and girls".