Hardline incumbent Mahmoud Ahmadinejad was heading for a landslide victory in Iran's presidential election, while his main moderate challenger denounced the results as "treason" and "dangerous manipulation."

Preliminary results on Saturday showed President Ahmadinejad receiving nearly double the votes of reformist rival Mir Hossein Mousavi.  The results give the incumbent 63 percent to about 34 percent for Mr. Mousavi, a former Iranian prime minister.

Mr. Mousavi issued a statement saying he "strongly protested" what he described as many violations in Friday's vote.  He vowed not to surrender to the "charade."

Security was tight throughout Tehran Saturday as people waited for final results to be announced.  Supporters of Mr. Mousavi briefly clashed with police in a Tehran square.

The initial results surprised many analysts who predicted a tight race between the incumbent president and Mr. Mousavi, with voters turning out to the polls in massive numbers Friday.

Election commission chief Kamran Daneshjou said turnout was "unprecedented."  Officials predicted a turnout of 70 percent or more of Iran's 46 million eligible voters.  Officials extended voting hours to accommodate long lines at polling stations.

Reformist cleric Mehdi Karroubi and conservative former Revolutionary Guards commander Mohsen Rezaei also competed in the poll, in which Iran's economy, nuclear program and foreign relations were said to play a key role.

Mr. Ahmadinejad's rivals have accused him of badly mismanaging the economy and tarnishing Iran's image, further isolating the country from the West.  The Iranian president has denied the Holocaust and called for Israel to be wiped off the map.

Saturday, Israel's Deputy Foreign Minister Danny Ayalon said the election results depicting Mr. Ahmadinejad's victory demonstrate that the "Iranian threat" has grown.  Ayalon also said the international community must stop the nuclear program and terrorism coming from Iran.

Some information for this report was provided by AFP, AP and Reuters.