Iran's six presidential hopefuls are wrapping up their final day of campaigning ahead of Friday's elections.
Momentum has recently been building around moderate cleric Hassan Rowhani.
But he faces a tough challenge from hardline candidates like top nuclear negotiator Saeed Jalili and Tehran mayor Mohammad Baqer Qalibaf.
The election will decide a successor to incumbent Mahmoud Ahmadinejad, who is not eligible for a third term.
His eight years in power have been characterised by economic turmoil and Western sanctions against Iran over its controversial nuclear programme.
Iran's Supreme Leader, Ayatollah Ali Khamenei, has called on all Iranians to vote.
"Whoever is elected, if he enjoys a strong and overwhelming vote, he will be able to stand up against enemies and aggressors more properly," Ayatollah Khamenei's website quoted him as saying.
The surge of support for Mr Rowhani came after Mohammad Reza Aref, the only reformist candidate in the race, announced on Tuesday that he was withdrawing his candidature on the advice of the pro-reform ex-president Mohammad Khatami.
Mr Rowhani now has the endorsement of two ex-presidents, Mr Khatami and Akbar Hashemi Rafsanjani.
Most of the other remaining candidates in the poll are conservatives close to Ayatollah Khamenei.
Friday's election is the first since 2009, when protesters took to the streets in anger at the results which they said had been rigged in favour of Mr Ahmadinejad.
The opposition says more than 80 of its supporters were killed in a crackdown over the following six months, a figure the government disputes. Several have been sentenced to death, and dozens jailed.
The two reformist candidates from 2009 - Mir Hossein Mousavi and Mehdi Karroubi - remain under house arrest.