(This post was last updated at 3:45 p.m. ET)

Hasan Rowhani, the lone moderate in Iran's presidential elections, has secured victory and headed off a runoff vote in a symbolic rebuke to the country's hard-line Islamic clerics.

Rowhani, 64, won nearly 51 percent of the vote in a field of five other candidates, all but himself considered conservatives who were more or less in line with Supreme Leader Ayatollah Ali Khamenei. Rowhani's closest rival, Tehran Mayor Mohammad Baqher Qalibaf, came in a distant second, with less than 17 percent of the ballots.

Iran's Interior Minister, Mostafa Mohammad-Najjar, announced Rowhani's victory on state television. Najjar said turnout among the country's 50 million eligible voters was more than 72 percent.

The candidate considered to be Khamenei's pick for the job, former Foreign Minister Ali Akbar Velayati came in fifth.

Rowhani (pronounced roh-HAH'-nee) will replace the combative Mahmoud Ahmadinejad, who was re-elected to a second term in 2009 amid accusations of a rigged election.

NPR's Peter Kenyon, reporting from Istanbul, says the announcement came "after a long, surprising day of vote counting."

He says "conservatives had hoped to keep Rowhani under the 50 percent threshold, forcing a runoff" with Qalibaf.

Reuters reports that Iranians "reveled in having delivered their message" to Khamenei. The news agency said:

"From the streets of Tehran came reports of a festive atmosphere, as crowds of [Rowhani] supporters dressed in his campaign [color] purple gathered to celebrate his emphatic victory.

Some chanted 'Ahmadi bye bye' heralding the imminent end to incumbent Ahamadinejad's presidency."

The White House on Saturday issued a statement congratulating Iranians "for their participation in the political process, and their courage in making their voices heard."

"It is our hope that the Iranian government will heed the will of the Iranian people and make responsible choices that create a better future for all Iranians," the statement read.

Who Is Rowhani?

The only cleric in the six-person race, Rowhani has been active in Iranian politics since the days of the Islamic Revolution, when he became a supporter of Ayatollah Ruhollah Khomeini, who in 1979 led the overthrow of the U.S.-backed shah.

Following the revolution, Rowhani was placed in charge of reorganizing Iran's military; he was also later a member of parliament and oversaw the state-run broadcaster. From 1989-1997, Rowhani served as President Akbar Hashemi Rafsanjani's national security adviser.

In 2003, Rowhani became the head of the influential Supreme National Security Council and took up duties as Iran's chief nuclear envoy amid tensions with the West over Tehran's burgeoning program.

But two years later, he had a falling out with Ahmadinejad over a decision to suspend uranium enrichment in an effort to forestall international sanctions. Ahmadinejad strongly opposed the move.

Rowhani subsequently backed Rafsanjani against Ahmadinejad in the 2005 election. He continues to maintain close ties with Rafsanjani, himself viewed as a key moderate. Rafsanjani had sought the presidency this time, but was summarily disqualified by Iran's powerful ruling clerics.

Speaking at a recent campaign rally, Rowhani said his goal was "constructive interaction with the world" that includes moves to end punishing U.N. Security Council sanctions, The Associated Press reports.

At the rally, he said Iran's leadership were proud of bringing sanctions on the country.

"I'll pursue a policy of reconciliation and peace. We will also reconcile with the world," he said.

But Rasool Nafisi, an Iranian affairs analyst at Strayer University in Virginia, speaking to the AP cautioned that Rowhani's reformist tendencies only go so far.

"Rowhani is not an outsider," he said. "The ruling system has made sure that no one on the ballot is going to shake things up."

As we reported on Friday, the president in Iran has little say in the country's most substantive issues. Most of the power is instead held by Supreme Leader Ayatollah Ali Khamenei, a hard-liner who did not favor Rowhani.

The Associated Press adds:

"Although all key policies such the nuclear program are directed by the ruling clerics, the alliance with Rafsanjani may give Rowhani more latitude to put his stamp on Iran's negotiation tactics with world powers after four rounds of talks since last year have failed to make any significant headway."

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