“I’m warning that I won’t surrender to this manipulation,” he said, adding that the election outcome “is nothing but shaking the pillars of the Islamic Republic of Iran sacred system and governance of lie and dictatorship”.

He warned “people won’t respect those who take power through fraud” and said the decision to declare Ahmadinejad the winner was a “treason to the votes of the people”.

The conflicting claims, coming after an extraordinary campaign that saw vast street demonstrations and vitriolic televised debates, seemed to undermine the public legitimacy of the vote and to threaten unrest.

The emotional campaign was widely seen as a referendum on Ahmadinejad’s divisive policies. It pitted Moussavi, a former Prime Minister who has pledged to move Iran away from confrontation with the West, combat economic stagnation and expand women’s rights, against Ahmadinejad’s economic populism, social conservatism, and hardline foreign policy.

At his news conference, Moussavi cited irregularities that included a shortage of ballots. He accused the Government of shutting down websites, newspapers and text messaging services throughout the country, crippling the opposition’s ability to communicate during the voting.

Fraud has been a prominent concern for Moussavi’s campaign, with many of his allies warning that Ahmadinejad could use the levers of state — the military, the Revolutionary Guard, and the Basij militia — to cajole or intimidate voters.

At his news conference, Moussavi called on the country’s supreme leader, Ayatollah Ali Khamenei, to help the country reach a “favourable conclusion”.

Amid the confusion overnight, a reformist website called Fararu said Moussavi was talking with the two other candidates, Karroubi and Rezai, to discuss the situation.