In a campaign speech in the western city of Hamedan, Rohani said on May 8 that voters did not want someone who in the four decades since Iran's revolution has only known how to "execute and jail."

That appeared to be a reference to hard-line candidate and cleric Ebrahim Raisi, who is said to have condemned many political opponents and opposition activists to death during a spate of thousands of summary trials in the 1980s.

Raisi spent years in senior regional and national posts in Iran's powerful judiciary, which plays a key role in enforcing state repression and silencing critics.

Iranian political analyst Taghi Rahmani called Rohani's tactic potentially "risky," because it could anger powerful hard-line interests, including within the Islamic Revolutionary Guards Corps (IRGC), a branch of the military, and the judiciary.