As a warning to moderates like President Hassan Rouhani, who championed the nuclear deal as necessary to revive Iran’s crippled economy and promised more freedoms when he was elected, Guards agents have started rounding up journalists, activists and cultural figures. In recent days, the intelligence unit arrested several prominent people, including Isa Saharkhiz, a well-known journalist and reformist; Ehsan Mazandarani, the top editor of a reformist newspaper, Farhikhtegan; and Afarin Chitsaz, an actress and newspaper columnist.

Image President Hassan Rouhani of Iran. Credit... Office of the Iranian Presidency, via Anadolu Agency

Other politically motivated arrests snared Siamak Namazi, an Iranian-American consultant known for his advocacy of improved ties with the United States, and Nizar Zakka, a Lebanese-American information technology expert. Even before the nuclear deal, three other Iranian-Americans were languishing in prison: Jason Rezaian, who is The Washington Post’s Tehran correspondent; Amir Hekmati; and Saeed Abedini. An unidentified operative working for the Guards went on state television this week to boast about dismantling a network of journalists working against the national interests.

Iran’s supreme leader, Ayatollah Ali Khamenei, is fueling the crackdown. He allowed the nuclear deal to proceed, but has since denounced the United States as Iran’s chief enemy and warned against what he says is America’s intention to infiltrate Iran and attack the country’s revolutionary roots.

In an important and surprisingly frank statement on Wednesday, Mr. Rouhani criticized the arrests and suggested that at least some of them were groundless. On his website, he called on the security and intelligence authorities to stop “toying with terminology” used by Ayatollah Khamenei to justify their actions.

Mr. Rouhani seems to be walking a fine line, trying to keep the nuclear deal on track with an eye to helping his allies in February’s parliamentary election, which is viewed as a public referendum on his tenure. He needs the cooperation of Ayatollah Khamenei and the Revolutionary Guards to carry out the nuclear deal, and experts say that limits his ability to challenge them on human rights.