Iran's outgoing president has warned of an organised dirty tricks campaign to disrupt the presidential election.
Young campaigners have made the most of a relaxed atmosphere
Mohammad Khatami's concerns were raised as campaigning ended before vote, which takes place on Friday.
"It seems there is an organised movement to hurt the glorious process of the elections," he said in a letter quoted by the official media.
Front-runner Akbar Hashemi Rafsanjani faces a tough challenge from two rivals meaning a run-off vote may be needed.
Mr Khatami did not identify who was behind the interference, which he said included "disruption of gatherings, beatings, illegal pamphlets and spreading lies to ruin candidates' reputations regardless of political inclination".
In addition to violence on the campaign trial, Iran has been rocked by a series of bombings in recent days that left up to 10 people dead.
Mr Rafsanjani has denounced an alleged dirty tricks campaign against him.
From 0900 (0430 GMT) on Thursday all electioneering is banned and candidates' teams must remove posters and campaign material from near polling stations.
Campaigning reached a climax in the early hours of Thursday, with many young men and women taking the opportunity to stay out late and mingle in a relaxed atmosphere not normally permitted in Iran.
With half of the country's 67 million population under 25 and voting permitted to 15-year-olds - all the candidates have been appealing to the youth vote.
Mr Khatami was swept to victory in 1997 on a reformist ticket.
But apathy has taken hold in Iran after his programme failed to deliver change in the face of the conservative religious establishment which is able to veto legislation and political candidates.
One candidate, former revolutionary guards chief Mohsen Rezai, pulled out of the race on Wednesday, apparently give more chance to his fellow right-wingers.
Mr Rezai said he was withdrawing from the race "based on the opinions of senior religious leaders", Iranian TV quoted him as saying, but he did not endorse another candidate.
The remaining seven candidates are a mix of conservative and reformists. Mr Rafsanjani - who was president between 1989 and 1997 - is seen as one of the most likely to appeal to voters on both sides of the spectrum.
In Mashhad, Iran's second city, many said they would back local man and former hardline police chief Mohammad Baqer Qalibaf.
Expert projections suggest most votes will be shared between Mr Rafsanjani, Mr Qalibaf and reformist Mostafa Moin, with no one polling more than the 50% needed to win in the first round.
A second round could be held on 1 July - which would be the first run-off in the Islamic republic's history.
Mr Moin's supporters say a high turnout would benefit him, but many young people and reformists are too disillusioned with the political and economic situation to bother voting.