Hardline incumbent Mahmoud Ahmadinejad won on Saturday a landslide win in Iran's presidential race, crushing his moderate rival and Western hopes of change in the Islamic republic.
Ahmadinejad won Iran's most hotly contested presidential election with 63 percent of the vote, Interior Minister Sadeq Mahsouli announced.
In second place behind the hardline incumbent was moderate ex-Prime Minister Mir Hossein Mousavi with 34 percent vote, he said. About 80 percent of Iran's 46 million eligible voters turned out to cast ballots.
However signs of tension emerged as his main challenger Mousavi cried foul over election irregularities and some of his supporters were beaten by baton-wielding police, an AFP correspondent said.
Ahmadinejad was assured of victory after election commission chief Kamran Daneshjoo said he had won almost 22 million votes or over 63 percent of the total with most districts counted.
Mousavi, one of Ahmadinejad's three rivals in the most heated election campaign since the Islamic revolution, had also declared himself the victor, well before official results were released, suggesting a tense feud ahead.
The international community has been keenly watching the election for any signs of a shift in policy after four years of hardline rhetoric from the 52-year-old Ahmadinejad and a standoff over Iran's nuclear drive.
Mousavi "strongly protest[ed]" against what he described as many violations in Iran's presidential election, in a statement issued Saturday.
"I personally strongly protest the many obvious violations and 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.
Mousavi, who late on Friday said he had won the election, called the official result of the vote "stunning."
"People who waited in long queues, they know the composition of the votes and they themselves know who they voted for," his statement said. "They are surprised and are watching the juggling of...officials when they announced the result."
He added that he would reveal the "secrets behind this dangerous charade" and said "I'm suggesting officials stop this trend before it is too late and return to the land of law and preserve people's rights."
Mehdi Karroubi the other reformist candidate declared the result of the election was "illegitimate and unacceptable."
But the Islamic Republic's election commission said Ahmadinejad was ahead with 65 percent of the votes from Friday's presidential election in the world's fifth biggest oil exporter after more than 30 million ballots had been counted.
Trita Parsi, president of the Washington-based National Iranian American Council, expressed disbelief at the wide margin in Ahmadinejad's favor.
"It is difficult to feel comfortable that this occurred without any cheating," Parsi said.
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 in the run-up to Friday's vote, might react to an Ahmadinejad victory. U.S. strategic intelligence group Stratfor called the situation "potentially explosive," with a considerable risk of unrest.
Scuffles broke out early on Saturday between police and chanting Mousavi supporters in a Tehran square. Police said they have increased security across the capital to prevent any trouble. All gatherings have been banned until the publication of final results.
Shortly before voting ended, some Tehran residents said they were unable to make international phone calls and some Internet servers went down.
Ahmadinejad's support came from from rural areas or poorer big city neighborhoods while Mousavi enjoyed strong backing in wealthier urban centers, and was expected to attract votes from women and young Iranians.
Ahmadinejad won power four years ago on a pledge to revive the values of the 1979 Islamic revolution. He has steadily built up Iran's nuclear program, rejecting Western charges that it is aimed at building an atomic bomb, and stirred international outrage by denying the Holocaust and calling for Israel to be wiped from the map.
Mousavi, 67, rejected Western demands that Iran halt uranium enrichment but analysts said he would have brought a different approach to Iran-U.S. ties and nuclear talks. Ultimately, however, nuclear and foreign policy are determined by the country's supreme leader, Ayatollah Ali Khamenei.
The United States has had no ties with Iran since shortly after the revolution but Obama said in Washington the United States had "tried to send a clear message that we think there is the possibility of change" in relations.