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.”