UNITED NATIONS — Executions have surged in Iran and oppressive conditions for women have worsened, a United Nations investigator said on Monday, drawing attention to rights abuses just as Iran’s president is pushing for a diplomatic breakthrough with the West.

The investigator, Ahmed Shaheed, a former diplomat from the Maldives and now special rapporteur on human rights in Iran, made the comments on the eve of presenting his latest findings to members of the United Nations General Assembly.

Mr. Shaheed said he had been shocked by the execution on Saturday of Reyhaneh Jabbari, 26, who was convicted of killing a man she had accused of raping her. The death sentence had prompted international outcry and efforts by the Iranian president, Hassan Rouhani, to rescind it. Under the Iranian Constitution, the president has no power over the judiciary.

In a briefing with reporters Monday morning, Mr. Shaheed suggested that Mr. Rouhani had only “limited authority” to make the broad changes that he promised when elected in June 2013.