"These kind of comments are mostly campaigning, and you cannot accurately assess and appraise these comments. We have to see which candidate gets elected and then see their policies in practice. This is campaigning and nothing new," foreign ministry spokesman Hamid Reza Asefi told reporters.

Under Kerry's proposal, outlined last week by his vice presidential running mate John Edwards, Washington would lift its objections over Tehran's construction of nuclear power plants for civilian use if Iran agreed to abandon its efforts to keep nuclear fuel that can be used to make weapons.

If the Islamic republic rejected the terms of Kerry's offer, the United States would consider it a confirmation of Tehran's nuclear bomb ambitions, he said. The United States would call on European allies to impose heavy sanctions on Iran if it failed to comply.

The proposal appears to be broadly similar to the approach adopted by the Europeans, who want Iran to renounce its bid to master the sensitive nuclear fuel cycle and the enrichment of uranium.

Fuel cycle work to provide fuel for reactor is permitted under the nuclear Non-Proliferation Treaty (NPT), even though it could be easily redirected towards military purposes.

Kerry's approach is a shift from President George W. Bush's policy, aimed at having Iran hauled in front of the UN Security Council for possible sanctions.

The Republican president's administration opposes the activation of Iran's power plant in the Gulf port of Bushehr, which Tehran says is being built exclusively for civilian purposes.

Washington believes Iran, one of the world's largest oil suppliers, has no need for nuclear energy and accuses Tehran of hiding a nuclear weapons development program under the guise of a civilian atomic energy programme.

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