A U.N. rapporteur on human rights in Iran has denounced executions of minors there and says tough anti-drugs laws could be behind a "surge" in overall executions in recent years.

Ahmed Shaheed, in a 21-page report released Thursday, cited Iran Human Rights Documentation Center figures showing 966 people were executed last year, up from 697 in 2013 and 91 in 2005. His report said more than 500 last year were related to drug law violations.

Shaheed said executions of juvenile offenders were "strictly and unequivocally prohibited" under international law. He said at least 73 had been executed in Iran between 2005 and 2015, the highest number of any country in that span.

Shaheed has not been allowed to visit Iran as part of his mandate, now in its fifth year.