Iran's supreme leader urged voters on Wednesday to turn out in large numbers for the June 18 presidential election, saying such a show of strength would reduce foreign pressure on the Islamic Republic.

Axar.az reports citing foreign media that two hardliners and one moderate quit the field of seven officially permitted candidates on Wednesday, leaving what is shaping into a straightforward contest between the hardline head of the judiciary and a moderate former head of the central bank.

Judiciary chief Ebrahim Raisi, 60, an ally of Supreme Leader Ayatollah Ali Khamenei, is widely tipped as the favourite to succeed Hassan Rouhani, a pragmatist stepping down after two terms.

"In less than 48 hours, a crucial event will take place in the country... By your presence and vote, you actually determine the fate of the country, in all major issues," Khamenei said in a televised speech.