GENEVA — He was a prosecutor of Iran’s Islamic revolution and acquired a notorious reputation for the arbitrary executions of thousands of opponents. A few decades later he oversaw the judiciary’s 2009 trials of anti-government protesters and was denounced overseas, not least by the United Nations.
But on Tuesday the former prosecutor, Seyyed Alireza Avaei, now Iran’s minister of justice, appeared at the United Nations Human Rights Council in Geneva, one of nearly 100 ministers and dignitaries to speak at the start of its main session this year. The reaction inside and outside the council was outrage.
Sweden’s foreign minister, Margot Wallstrom, and a handful of European diplomats left the council chamber in protest.
Had the meeting been held in a European Union member state Mr. Avaei would have not been permitted to attend. The European Union penalized Mr. Avaei with a travel ban and assets freeze in October 2011 for “human rights violations, arbitrary arrests, denials of prisoners’ rights and increase of executions.”
Outside the United Nations offices, several dozen Iranian opponents of Iran’s government, mostly from Switzerland and France, noisily denounced Mr. Avaei’s appearance, the 1988 “massacre” in which he played a prominent part and the repression of critics and dissidents.
The council will vote in March on whether to reappoint a human rights expert to monitor Iran’s conduct, an arrangement fiercely resented by Iran.
Mr. Avaei seized the opportunity to denounce what he called the domination and manipulation of international human rights mechanisms by countries like the United States.
He said the council should apply “cherished principles of objectivity, impartiality, transparency and consensus” to thwart what he described as those countries’ double standards and the politicization of the council’s proceedings.
Defending Iran’s record, Mr. Avaei said the government had thoroughly revised its penal code and criminal procedures to increase safeguards and rights of the accused.
He also said amendments to Iran’s strict narcotics laws, the basis for most of the country’s executions, were reducing the use of capital punishment.
Although executions in Iran have fallen in recent years, the number still carried out remains among the world’s highest.
Concern also has increased recently over the deaths in detention of several protesters arrested at anti-government demonstrations. The most prominent case is the death of an Iranian-Canadian environmentalist, Kavous Seyed Emami. Days after his arrest, apparently on suspicion of spying, the authorities told his family that he had committed suicide.
In January, the United Nations human rights chief, Zeid Ra’ad al-Hussein, criticized Iran for flouting the international prohibition on executing people who were juveniles when they were accused of the offenses for which they were detained — five in 2017 and three in January, with at least 89 more waiting on death row.
Mr. Avaei’s speech at the council came just as the United Nations released an annual report by Secretary General António Guterres on human rights in Iran, detailing a wide range of abuses.
Courts continue to sentence defendants to punishment by flogging and amputation, freedom of expression remains sharply restricted and human rights advocates and journalists face harassment, intimidation and imprisonment.
Mr. Avaei’s appearance was “an insult” to the memory of victims of his trials and to human rights defenders, said Impact Iran, a coalition of nongovernment groups monitoring human rights in Iran.
“By choosing a major violator as Iran’s voice on human rights,” it said in a statement, “Iran is also making a mockery of the Human Rights Council and showing contempt for the U.N. human rights system as a whole.”