Tehran Mayor, Mohammad Bagher Ghalibaf quit the Iranian presidential race on Monday, backing instead hardline cleric Ebrahim Raeisi in Friday's presidential vote.

"I should take an important decision to keep the unity of revolutionary forces... I ask all my supporters around the country to use all their capacity to help my brother, Mr Ebrahim Raeisi win the election," Ghalibaf said in a statement published on the Iranian Student News Agency, ISNA.

Ghalibaf, a former Revolutionary Guards commander and police chief, was one of main rivals of president Hassan Rouhani who is seeking a second term.

Ghalibaf's future as mayor of Tehran depends on the outcome of local elections on Friday, May 19. If reformists win a majority in the Tehran city council, Ghalibaf might be replaced in the future. Another possibility for him is to get a high level appointment in case of a Raeisi victory in the presidential race.

It was anticipated that some of the six candidates who were approved by the regime to run for president would quit before the vote in favor of two main candidates, Rouhani and Raeisi. Now, the first move was made in the conservative camp, with Ghalibaf announcing his withdrawal from the race.

The next person to do the same will probably be Eshagh Jahangiri, Rouhani's deputy who is widely believed to have entered the race to help the incumbent in the campaign's political battle with the conservatives. Jahangiri had a strong presence during the three presidential debates, often citing statistics and using arguments that put the conservative candidates in a more difficult spot.

In another development, Mehdi Karoubi, one of the symbols of Iran's dissident Green Movement, who has been under house arrest for years, called on people to vote for Hassan Rouhani. He urged voters to cast their ballots for their favorite candidates, but added that personally, he would vote for Rouhani. He voiced concern that the "republican" nature of Iran's political system can be in danger if the incumbent is not re-elected.

Rouhani, who is visiting various cities for campaign appearances, accused his opponents on May 15 that they pass on "lies" to the Supreme Leader, ayatollah Ali Khameni about his government. He was speaking in the northwestern city of Tabriz.

Raeisi and Ghalibaf have been accusing Rouhani of reneging on most of his economic promises and has neglected the working classes.