At least 850 people have been executed in Iran in the past 15 months as part of a worsening human rights situation under reformist President Hassan Rouhani, a UN official said Monday.
Ahmed Shaheed, the rights rapporteur for Iran, described a "surge in executions," giving Iran the world's the highest death penalty rate per capita.
"The range of capital crimes is shocking," Shaheed told journalists. "We have seen a person executed for making a donation to a foreign organization."
The rapporteur said he was "shocked" by the hanging over the weekend of 26-year-old Reyhaneh Jabbari who was convicted of murdering a former intelligence officer she claimed had tried to sexually assault her.
Shaheed said he had repeatedly raised with Tehran questions about the fairness of her trial.  
Iran has executed 852 people since June of last year, including eight juveniles, said the envoy, who is to present his report to the UN General Assembly on Tuesday.
The surge in executions shows that Rouhani has failed to deliver on campaign promises to improve the human rights situation in his country, a year after taking office, he said.
"He is unable to address the issues, unable to arrest this trend, to convert his promises which spoke to arresting this trend into action," said Shaheed.
The rapporteur suggested that Rouhani lacked political backing, in particular from parliament, to advance his rights agenda.
Since his appointment in 2011, Shaheed has never been allowed to visit Iran, but he has spoken to some 400 Iranians, making use of Skype and at times even receiving calls from prison.
Shaheed conveyed the concern from many Iranians that ongoing negotiations on Tehran's nuclear program had allowed human rights to be placed on the back burner.
But the envoy said he had not seen a shift in emphasis from the United States and the West on human rights and that southern countries like Brazil and South Africa were also raising these issues with Tehran.
In his report to the 193-nation Assembly, Shaheed also raised concerns over freedom of the press, noting that 35 journalists are currently behind bars in Iran.
At least 300 people are in prison for their religious practices including 120 Bahais and 49 Christians.
The report also touched on a drop in the number of women enrolled at universities, from 62 percent in 2008 to 48 percent last year.
A UN General Assembly is expected next month to vote on a draft resolution put forward by Canada and other nations condemning rights abuses in Iran.