Iran's Interior Ministry has announced moderate candidate Hassan Rohani has won the country's presidential election.

Interior Minister Mohammad Mostafa Najjar announced on television on June 15 that Rohani had received 18.6 million votes, or 50.68 percent of the ballots, sufficient to win outright, avoiding the need for a second round of elections.

Rohani was far ahead of the five other candidates running for president, with his closest rival, Tehran Mayor Mohammad Baqer Qalibaf, receiving less than 16 percent of the vote.

Interior Minister Najjar said 36.7 million people, or 72.7 percent of the country's total electorate, cast ballots in the June 14 election.

Authorities extended voting hours several times. Iran is estimated to have 50 million eligible voters.

Voters were choosing between six candidates to replace President Mahmud Ahmadinejad, who has served the maximum two consecutive terms. All six were approved to campaign by the conservative, unelected Guardians Council.

Iran's Supreme Leader Ayatollah Ali Khamenei said on Twitter on June 15 that a vote for any of the six candidates in the presidential race is a "vote of confidence in the system."

No international observers came to Iran to monitor the election process.

WATCH: Iranians across the country and abroad celebrate Hassan Rohani's election victory.

Rohani Supporters Celebrate Iran Election Victory

Interviews conducted by RFE/RL’s Radio Farda indicated Rohani was a favorite among most people such as this listener: "I voted for Rohani and I'm happy he is leading in the vote count."

Another Radio Farda listener expressed gratitude to former Presidents Akbar Hashemi Rafsanjani and Mohammad Khatami who supported Rohani in the presidential campaign.

"I am grateful to Mr. Rafsanjani and Khatami who supported Mr Rohani, and led the nation toward the right path. I hope Mr. Rohani will make Mr. Rafsanjani and Mr. Khatami proud."

But one listener in the city of Shiraz indicated the authorities had made it difficult to show support for Rohani.

"I live in Shiraz. Law enforcement forces have the city under strict control. If someone comes out to express their solidarity to Rohani, the law enforcement forces try to prevent them."

And another voter in Shiraz said Rohani faces a challenge trying to address the country’s many problems.

"Even if Mr. Rohani wins the presidency, and even he stays in office for ten years, he would still be not able to repair what was done during Ahmadinejad’s presidency. The country is a very bad shape now, and it takes time to fix things."

PHOTO GALLERY: Iranians Go To The Polls To Elect A New President

Iranians Go To The Polls To Elect A New President

Enforcing The Leader's Will

In the Islamic republic's political system, Iran's supreme leader, not the president, holds the ultimate decision-making power -- including commanding the army, directing foreign policy, and overseeing projects such as Iran's nuclear program.

Candidate Rohani has recently backed greater freedom of expression and pledged to free political prisoners.

He is also a former chief nuclear negotiator for Iran and supports the continuation of the country's controversial nuclear program. Many Western states say the program is being used as cover for building a nuclear weapon.

Former Iranian Presidents Mohammad Khatami and Akbar Hashemi Rafsanjani, as well as the supreme leader's younger brother, Hadi Khamenei, have thrown their support behind Rohani.

Mohammad Reza Aref, a reformist, received approval to campaign but withdrew from the race earlier this week to increase Rohani's chances of winning.

After casting his vote in Tehran, Khamenei dismissed those who questioned the democratic nature of the election.

"I recently heard that someone from America's National Security Council said, ‘We don't accept this election in Iran.' Well, to hell with you if you don't accept it," Khamenei said.

Khamenei did not make clear whom he was referring to. But last month U.S. Secretary of State John Kerry cast doubt on the credibility of the election following the disqualification of hundreds candidates, including those whom observers considered potential reformers and all the women who wanted to run.

Kerry criticized what he called a "lack of transparency" in the election process and said the disqualifications were "based solely on who represents the regime's interests."

With reporting by Press TV, Reuters, AP, and AFP