Haunted by 2009 bloody chaos, Iranians vote in presidential election Iran's presidential election Moderate candidate complains of voting irregularity Supreme leader to U.S. politicians: "Hell with their recognition!" Ayatollah Khamenei: "Go to ballot boxes as soon as possible" The last election resulted in bloody street protests known as the "Green Movement" Send us your thoughts and experiences of the election. (CNN) -- Television cameras zoomed in on his hand Friday as Iran's supreme leader filled out the very first ballot in the national election to replace outgoing President Mahmoud Ahmadinejad. Ayatollah Ali Khamenei slipped the folded paper into the ballot box and turned to the cameras. His vote officially opened the ballots as he called on the 50 million Iranians eligible to vote to pick one of six candidates in the "epic" election. "My expectation of our endeared people is for everyone to take part, and I would recommend that they go to ballot boxes as soon as possible and not to delay," he said. Iranians appeared to heed their leader's call, with voters flocking to the country's 60,000 voting stations. CNN's view on the streets of Tehran The Interior Ministry is extending voting hours to accommodate a high turnout, state-run Press TV reported. After the "Green Movement" uprising that flooded Tehran's streets following Ahmadinejad's reelection in 2009, the government has accused the West of urging some voters to boycott the polls. CNN's Erin Burnett on 2013 vs. 2009 elections 2009 chaos Images of bleeding and dying Iranians flickered across social media four years ago after allegations of voter fraud sparked protests and clashes. Police and the Basij, a feared paramilitary group, cracked down on the protests. Protesters were jailed, and human rights groups alleged many were tortured and killed behind bars while the government quashed the uprising. Reform politicians representing the movement, including Ahmadinejad's election rival, former Prime Minister Mir Hossein Moussavi, have remained under house arrest. Despite the unrest, Ahmadinejad's re-election was formally certified by the clerical establishment. Khamenei's office repeated his call to the ballot boxes Friday with posts on social networking site Twitter. "I humbly expect from our nation to participate all in #IranElection & do this as soon as possible," the supreme leader's post said. Voting is not mandatory in Iran, but there are major incentives to push people to the polls. An active voter has a better shot at promotions in the workplace and preference when it comes to collecting social welfare benefits. This can be vital in an economy that is chronically weighed down by international sanctions over nuclear concerns. Khamenei also tweeted a jab at the United States, which has often led the charge to tighten those sanctions. I have heard that #USpoliticians said they don't recognize #IranianElection. Hell with their recognition!" he said. Somewhat controlled All candidates are pre-approved to run for the nation's highest elected office by Iran's Guardian Council, a nonelected body made up of six clerics and six lawyers operating under the oversight of the supreme leader. It allows Khamenei to limit the election process. Out of 680 candidates, eight were approved. Two have dropped out of the race. The six remaining candidates are: Mohammad Bagher Ghalibaf, Ali-Akbar Velayati, Saeed Jalili, Mohsen Rezaei, Hassan Rouhani, and Mohammad Gharazi. Velayati, Ghalibaf and Jalili, who is Iran's chief nuclear negotiator, are considered close to the Khamenei and would be unlikely to challenge his authority. Of the three conservatives, Jalili has seen the most popular support going into the vote. Rouhani is considered a centrist and has the backing of the highly influential former President Akbar Hashemi Rafsanjani. Hours into the voting, Rouhani complained of a voting irregularity. A reform candidate, Mohammed Aref, who dropped out of the race earlier in the week, is still on some ballots. Centrist contender Rouhani is worried voters may mistakenly select Aref. It would amount to a vote thrown away. In a blow to Ahmadinejad, his aide and protege Esfandiar Rahim Mashaei, a reformist, was among those excluded by the Guardian Council. Since his re-election, conservative politicians close to the supreme leader have assailed Ahmadinejad for being too liberal, and he has often been at odds with Khamenei. Some of Ahmadinejad's associates have faced heavy repressions, and hardliners attempted to link the president to the largest embezzlement case in the country's history. CNN's Laura Smith-Spark contributed to this report