By Parisa Hafezi and Fredrik Dahl
TEHRAN (Reuters) - Hardline President Mahmoud Ahmadinejad won Iran's election by a thumping margin, according to official results which his moderate challenger rejected on Saturday as a "dangerous charade" that could lead to tyranny.
The level of the incumbent's support, nearly twice as many votes as former Prime Minister Mirhossein Mousavi with most ballots counted from Friday's poll, confounded widespread expectations that the race would at least go to a second round.
Mousavi protested against what he said were many obvious violations in Friday's presidential election.
"I'm warning I will not surrender to this dangerous charade. The result of such performance by some officials will jeopardise the pillars of the Islamic Republic and will establish tyranny," he said in a statement made available to Reuters.
Iranian and Western analysts abroad greeted the results with disbelief. They said Ahmadinejad's re-election would disappoint Western powers aiming to convince Iran to halt work they suspect is aimed at making bombs, and could further complicate efforts by U.S. President Barack Obama to reach out to Tehran.
"It doesn't augur well for an early and peaceful settlement of the nuclear dispute," said Mark Fitzpatrick at London's International Institute for Strategic Studies.
A bitterly fought campaign generated strong interest around the world and intense excitement inside Iran. It revealed deep divisions among establishment figures between those backing Ahmadinejad and those pushing for social and political change.
Ahmadinejad accused his rivals of undermining the Islamic Republic by advocating detente with the West. Mousavi accused him of humiliating Iranians with an "extremist" foreign policy.
Listing several complaints before official results were announced, Mousavi said late Friday that many people had not been able to vote and that there was a lack of ballot papers.
He also accused authorities of blocking text messaging, with which his campaign tried to reach young, urban voters.
"I am the definite winner of this presidential election," Mousavi told a news conference.
But the state election commission said Ahmadinejad had won a second four-year term with about 63.4 percent of votes against 34.7 percent for Mousavi with almost all ballots counted. It put the turnout at around 80 percent of 46 million eligible voters.
Trita Parsi, president of the Washington-based National Iranian American Council, expressed disbelief at the wide margin in Ahmadinejad's favour. "It is difficult to feel comfortable that this occurred without any cheating," Parsi said.
"The potential for unrest is high," said Ali Ansari, who heads the Institute for Iranian Studies at St Andrews University in Scotland. "People will wake up today in Iran in shock."
STREET SCUFFLES
Western capitals had hoped a victory for Mousavi could help ease tensions with the West, which is concerned about Tehran's nuclear plans, and improve chances of engagement with Obama, who has talked about a new start in ties with Tehran.
Now they must again deal with Ahmadinejad, who has refused talks with six world powers over Iran's nuclear program.
The three-week election campaign was marked by mudslinging, with Ahmadinejad accusing his rivals of corruption. They said he was lying about the state of the economy.
It was unclear how Mousavi's supporters, who thronged the streets of Tehran nightly during the campaign, might react to Ahmadinejad's victory. U.S. strategic intelligence group Stratfor called the situation "potentially explosive."
Scuffles broke out overnight between police and chanting Mousavi supporters in a Tehran square, a Reuters witness said. Police said they had boosted security across the capital. All gatherings have been banned until final results are declared.
Ahmadinejad draws his bedrock support from rural areas and poorer big city neighbourhoods. Mousavi enjoys strong backing in wealthier urban centres, especially among women and the young.
Two other candidates attracted only tiny voter support.
Turnout was heavy after a campaign marked by heated debate over inflation -- officially 15 percent -- and unemployment.
Ahmadinejad, 52, won power four years ago, vowing to revive the values of the 1979 Islamic revolution. He has expanded the nuclear program, rejecting Western charges that it is aimed at bomb-making, and stirred international outrage by denying the Holocaust and calling for Israel to be wiped from the map.
Mousavi, 67, rejects Western demands that Iran halt uranium enrichment but analysts say he would have brought a different approach to Iran-U.S. ties and talks on the nuclear issue.
Ultimately, however, Supreme Leader Ayatollah Ali Khamenei controls nuclear and foreign policy.
The United States has had no ties with Iran, the world's fifth biggest oil exporter, since shortly after the 1979 Islamic revolution. Obama said his country had "tried to send a clear message that we think there is the possibility of change."
(Additional reporting by Hossein Jaseb, Hashem Kalantari, Zahra Hosseinian in Tehran and Alistair Lyon in Beirut; Writing by Dominic Evans and Fredrik Dahl; Editing by Alistair Lyon)
