Mayor of Tehran Mohammad Baqer Qalibaf, a figure in the principlist political faction who struggled to drum up support for his presidential campaign by hammering Rouhani, chose to quit the race on Monday in favor of Raeisi.
The report said Tehran Mayor Mohammad Bagher Qalibaf made the decision to boost the chances of hard-liner Ebrahim Raisi, believed to be close to Supreme Leader Ayatollah Ali Khamenei.
Es'haq Jahangiri, the Iranian first vice president and a candidate in the country's 12th presidential election, has dropped out of the race to back moderate President Hassan Rouhani. That held true in 1997 with the election of reformer Seyyed Mohammad Khatami, who threw his support Monday behind Rouhani.
A Rouhani win would affirm and strengthen the nuclear deal, and it makes continued Iranian compliance more likely.
But it has struggled to attract the large-scale foreign investments Mr Rouhani promised when the deal came into force, and which he said were necessary to reduce unemployment and kick-start the economy.More news: South Korea's Moon warns high chance of clashes with North
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Jahangiri, a 60-year-old confidante of the moderate president, was a surprise last-minute entry for Friday's election.
Iranian elections are overseen by a clerical body that vets candidates and bars anyone seen as posing a challenge to Iran's unique brand of theocratic rule.
Having now called on conservative voters to unite behind Raisi, Qalibaf could conceivably upset forecasts that Rouhani was on course for a comfortable victory.
"Vote for Rouhani because he is the man for hard situations..." It was Khamenei who previous year appointed Raisi, 56, to manage the Astan Quds Razavi, an Islamic charity that controls assets worth billions of dollars, as well as the Imam Reza shrine in the northeastern holy city of Mashhad. "We have resolved some problems and bigger problems remain for us to resolve on this hard path with him", Khatami said in a video message, "It is now your turn to renew your vote for our dear Rouhani in order to strengthen hope for a better future". As many as 16.2 percent of the respondents said they had not yet decided whether to vote or not. Iran agreed to limit its enrichment of uranium in exchange for the lifting of some economic sanctions. While the lifting of nuclear-related sanctions has alleviated pressure on Iran's struggling economy, many European firms remain fearful of investing in Iran due to the remaining United States sanctions, some of which threaten to punish third parties that violate them.