TEHRAN (Reuters) -- A reformist cleric contesting Iran's presidential election says he will defy growing calls to stand aside and unify moderate voters against hard-line President Mahmud Ahmadinejad.
Mehdi Karrubi, the most liberal of Ahmadinejad's rivals in the June 12 election, is seen as an outsider in the race and has come under pressure from reformists to withdraw and boost the chances of former Prime Minister Mir Hossein Musavi.
"I will never withdraw," he told a news conference. "I believe the larger the number of candidates, the better."
But an ally said Karrubi, a former parliamentary speaker, was likely to face continued pressure to stand down in the next few days in order to avoid splitting the pro-reform vote.
Like Karrubi, Musavi accuses Ahmadinejad of isolating Iran with his vitriolic attacks on the United States, his combative line on Iran's nuclear policy, and his denial of the Holocaust.
He advocates easing nuclear tensions, while rejecting demands that Tehran halt nuclear work which the West fears could be used to make bombs. Iran, the world's fifth-largest oil exporter, says its nuclear program is peaceful.
The election will not change Tehran's nuclear policy, which is decided by Supreme Leader Ayatollah Ali Khamenei, but a victory for Musavi could pave the way to a less confrontational relationship with the West.
The United Nations has imposed three sets of sanctions on Iran over its refusal to suspend uranium enrichment, steps which Ahmadinejad has repeatedly brushed aside.
"Let the world know that if the Iranian nation should reelect this small servant, he would go forward in the world arena with the nation's authority and would not withdraw an iota from the nation's rights," Fars news agency quoted him as saying on June 9 in the Caspian Sea province of Mazenderan.
Musavi's campaign has gained momentum in the run-up to the vote after he clashed with Ahmadinejad in a heated televised debate last week.
But analysts caution against predicting the election outcome, especially after the relatively unknown Ahmadinejad unexpectedly won the presidency in 2005.
Despite criticism that his free-spending policies have fueled inflation and squandered oil revenues, he still has the backing of Khamenei and can mobilize support of the Basij, a religious volunteer force with millions of members.
Musavi will count on support of Iranians, particularly younger voters, disenchanted with Ahmadinejad's efforts to steer the country back to the Islamist austerity of the 1979 Revolution.
Thousands of Musavi's supporters have thronged the streets of relatively affluent northern Tehran in nightly demonstrations, dressed in his green campaign colors, waving his picture, and blocking traffic into the early hours.
Supporters of Ahmadinejad, Karrubi, and the fourth candidate, former Revolutionary Guard leader Mohsen Rezai, have also made their presence felt.
Tens of thousands of Ahmadinejad loyalists crammed into a huge mosque complex under construction in central Tehran on June 8, waiting hours in vain for him to show up.
"He raised Iran's honor and showed the Iranian nation's power to the world," said 20-year-old student Mohsen Alizadeh.
In last week's debate, Musavi accused Ahmadinejad of humiliating Iranians by pursuing an "extremist" foreign policy and lying about the economy, which has been hit by high inflation and a fall in oil revenues.
Ahmadinejad hit back, saying Mousavi and his backers, including reformist former President Mohammad Khatami, were trying to weaken Iran by seeking a policy of detente with the West.