Iranians will elect a new president on Friday, with all but one of the four candidates to succeed Hassan Rouhani regarded as hardliners.

Opinion polls suggest Ebrahim Raisi, a conservative Shia cleric who heads the judiciary, is the clear favourite.

Moderate former central bank governor Abdolnasser Hemmati is his main rival.

Dissidents and some reformists have called for a boycott, saying the barring of several contenders left Mr Raisi with no serious competition.

There is also widespread discontent among Iranians at the economic hardship they have faced since the US abandoned a nuclear deal with Iran three years ago and reinstated crippling sanctions.

A victory for one of the hardliners is not expected to derail talks in Vienna between Iran and world powers that are aimed at reviving the accord, which saw Iran agree to limit its nuclear programme in return for sanctions relief.