Both leading candidates declared victory in Iranian presidential elections on Friday after 16 hours of voting, as polls finally came to a close at midnight (1930 GMT).
Incumbent President Mahmoud Ahmadinejad was leading the polls capturing almost 70 per cent of the 20 per cent of ballots counted so far, the news network Press TV reported on Friday night.
Main challenger, Mir-Hossein Moussavi had gained 26 per cent of the counted votes, which were mainly from the provinces.
But Moussavi said in a press conference in Tehran that he was the clear winner of the votes, and accused the government of having made numerous legal violations.
Results were expected to trickle out throughout Saturday, the interior ministry reported.
Voters turned out in unexpectedly high numbers, leading officials to keep polls open for six hours longer than originally planned.
Moussavi, Mehdi Karroubi and Mohsen Rezaei are the three candidates challenging Ahmadinejad.
In the capital, Tehran, long queues formed even before the polling stations opened at 8 am, several witnesses said.
There are 8.7 million people eligible to vote in Tehran and its suburbs. According to official estimations, the turnout in the capital was double that in 2005.
The high participation early in the day confirmed predictions by the interior ministry that there would be a record turnout in this year's polls.
The ILNA news agency reported that even many "silent voters", referring to Iranians who had never voted before due to their opposition to the system, went to the polls this time.
Eyewitnesses confirmed the ILNA report and said that there have been a number of voters at the polls "whose identity card was totally blank". A special election page in the Iranian ID cards is stamped every time a vote is given. Iranians opposing the system say that any stamp in their ID card would mean acknowledgement of the Islamic republic.
Fars news agency reported that in villages, turnout reached record highs of 90 per cent. Turnout was also high in provincial cities.
The senate-like Guardian Council predicted the total turnout to be more than 70 per cent.
About 46.2 million Iranians out of a total population of 70.4 million are eligible to vote.
The Iranian police said in a statement that no violent incidents had been reported. However, according to unconfirmed reports, one of Moussavi's election headquarters in northern Tehran was attacked by four Ahmadinejad supporters who were eventually arrested.
The camps of Moussavi and Karroubi had voiced concern over probable infringement in the voting and later in the counting process, a claim which the interior ministry disputed.
Ahmadinejad, who cast his vote in a mosque in southeastern Tehran, said the huge turnout showed the voters' willingness to continue the path of "pride, progress and prosperity".
Moussavi and his wife, Zahra Ranhnavard, cast their votes in a mosque in southern Iran.
"This enthusiasm of the people reflects their willingness for change in Iran," Moussavi said.
According to opinion polls, Moussavi is Ahmadinejad's main challenger.
"I ask all my supporters to keep on voting, and if I am elected, I will try my best to solve the problems," Moussavi added.
Former president Akbar Hashemi-Rafsanjani said the election would help determine the country's future.
"In my opinion, this year's election is one of the most important in our country's history and will definitely have an important impact on Iran's future role in world developments," Rafsanjani said after casting his vote in northern Tehran.
Rafsanjani is one of the harshest critics of Ahmadinejad and backs Moussavi.
"Every single vote counts, and everybody should be aware of the important impact of his vote," the moderate cleric said.
There are 45,713 polling stations throughout the country and 304 for Iranians abroad, including 32 in the US.
Moussavi said that neither he nor his supporters would sleep until the results of the presidential election were announced.
Moussavi said on his website Qalam that the high turnout in the election was "a golden opportunity which should be used for reaching better and nicer days".
The former prime minister, who had chosen the colour green as his symbol for Islam, hope and change, further hoped that the "Green Wave" of his supporters will eventually lead to a political change in Iran.
If none of the four candidates receives an absolute majority in the first round of voting, a run-off will be held on June 19 between the two candidates with the most votes.