Hardline president Mahmoud Ahmadinejad resoundingly won Iran's election, preliminary official results showed today, but his moderate challenger alleged irregularities and claimed victory for himself.
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.
Mr Ahmadinejad's re-election is likely to disappoint Western powers aiming to convince Iran to halt work they suspect is aimed at making bombs, and could further complicate efforts by US 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 Mr Ahmadinejad and those pushing for social and political change.
Mr Ahmadinejad accused his opponents of trying to undermine the Islamic Republic through a policy of detente with the West. Mr Mousavi hit back by saying the conservative president had humiliated Iranians with his "extremist" foreign policy.
Listing several complaints before official results were announced, Mr Mousavi said late on 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," Mr Mousavi told a news conference.
But the state election commission said Mr Ahmadinejad had won about 63.8 percent of the votes from the election in the world's fifth biggest oil exporter, with 38 million counted.
Mr Mousavi had around 32.7 percent support, said the commission. Based on an Interior Ministry estimate of more than 80 percent turnout of Iran's 46 million eligible voters, he could not beat Mr Ahmadinejad with the votes still to be counted.
Trita Parsi, president of the Washington-based National Iranian American Council, expressed disbelief at the wide margin in Mr Ahmadinejad's favour. "It is difficult to feel comfortable that this occurred without any cheating," Ms Parsi said.
Speaking in Washington before the results were released, US President Barack Obama said his administration was excited about the debate taking place in Iran and he hoped it would help the two countries to engage "in new ways".