GENEVA — Iran’s use of the death penalty is rising and its repression of political critics is worsening despite promises by President Hassan Rouhani of a less restrictive society, a United Nations human rights monitor said on Monday.

The monitor, Ahmed Shaheed, also raised the possibility that the human rights situation in Iran could improve if progress is achieved in overall relations between Iran and Western governments, a possibility at the current talks on Iran’s disputed nuclear program.

Iran has one of the highest execution rates in the world and continues “to harass, arrest, prosecute and imprison members of civil society who express criticism of the government or who publicly deviate from officially sanctioned narratives,” Mr. Shaheed told reporters in Geneva.

He spoke before delivering one of his periodic reports on Iran to the United Nations Human Rights Council.