Karoubi asked all Iranians to participate in the election and to protect the democratic process by choosing their preferred candidate, but said: "I will vote for Rouhani", Saham News, the official website of his political party reported on Monday.
A survey conducted by the Information Agency of the Islamic Republic (IRNA) on May 7-8 revealed that about 66.7 percent of respondents will participate in the presidential elections on May 19 in Iran.
"Mousavi! Karroubi! Khatami!" they chanted at deafening volume, over and over, at the election rally in a stadium in western Tehran.
Speaking at a gathering in the mainly Kurdish populated city of Urmia in northwest of Iran, Raisi said he saw no differences between the country's diverse peoples and faiths.
Meanwhile, the crowd in the stadium, estimated at way over 12,000, called out the names of Mir Hossein Mousavi and Mahdi Karroubi, opposition leaders who are now under house arrest, and Mohammad Khatami, former Iranian pro-reform president who is under a media blackout by the establishment, reported Reuters. The deal's sanctions relief has apparently not been enough for some within Iranian politics, as Rouhani has been criticized for failing to make good on his promises.
President's also have tremendous influence over the economy.
Although he has long cast himself as an insider and pragmatist rather than a gung-ho reformer, he seems to have shed that more moderate image in recent days, seeking to energise voters who want less confrontation overseas and more freedom at home.
Presidents can serve up to two consecutive four-year terms.
Ghalibaf took just over 6m votes in the 2013 presidential election, which was won in the first round by Rouhani with 18.6m votes and 50.71% of the vote share. Out of 1,600 people who registered to run in this year's presidential elections, the Guardian Council approved six people. If no candidate wins the majority, a run-off between the two lead contenders will take place a week later.
Who are the leading candidates for president? .
Khatami was banned from publishing public statements in the media after he openly supported mass protests which occurred due to alleged fraud in votes' counting in the 2009 presidential election.
However, most Iranians have yet to see the benefits of the nuclear deal.
The main challenger Raisi is a close ally and protege of Khamenei, and was one of four Islamic judges who ordered the execution of thousands of political prisoners in 1988. So in the end, this is a decision by the highest power in Iran.
"Many issues have been resolved but bigger issues remain, which we must all help to solve", he said in the video published on his Telegram messenger account.
That's exactly the kind of voter Rouhani needs to inspire.
Rouhani insinuated the top hard-line candidate he faces, Ebrahim Raisi, of being in the pocket of the paramilitary Revolutionary Guard.
The news Qalibaf was standing down broke as Raisi was delivering a speech in Shiraz, thrilling his supporters.
Will the election affect U.S. -Iran relations? But experts are concerned about how a conservative candidate will interact with President Donald Trump. However, the Iranian opposition claims, the opposite, arguing that little has changed during Rouhani's presidency.
"Of course, the other sides should also show goodwill and fairness, so we can work out other problems, as we did it before", he said.