U.S. officials have already dismissed the idea, floated last week by Russia. On Sunday, the U.S. and Russian presidents said they had narrowed their differences over Iran at a meeting in St Petersburg. But Moscow has yet to heed Washington's pleas that it stop building Iran's first nuclear reactor, at Bushehr.

Having taken over Iraq, U.S. President George W. Bush has increased pressure on the rest of his "axis of evil", Iran and North Korea, accusing them of developing nuclear weapons, though stopping well short of threatening Iraq-style military action.

Unlike North Korea, Iran denies seeking nuclear arms. But U.S. officials question why else the oil-and gas-rich Islamic republic would be investing in power-generating reactors.

Asefi told a news conference Washington was simply using the reactor programme as a "pretext to put pressure on Iran", with which it has been at odds since the Islamic revolution of 1979.

He said Tehran welcomed Russian President Vladimir Putin's call on Sunday for tighter controls on atomic weapons:

"We totally agree with Putin's remarks regarding weapons of mass destruction. Iran was the first country that suggested the whole region must be void of such weapons," Asefi said. "Russia has acknowledged our nuclear activities are peaceful."

Iran is a signatory to the nuclear Non-Proliferation Treaty, but has yet to sign the Additional Protocol, which allows U.N. inspections with minimal advance notification.

Analysts say Iran's signing of the Additional Protocol would go a long way to ease concerns over Tehran's nuclear intentions.

"We will sign it when the current limitations and embargoes are lifted and when we make sure that signing another agreement will not impose more limitations to Iran," he said.

Iran's suggestion of U.S. cooperation in its civil nuclear programme bears some comparison with a 1994 deal under which the United States agreed to give North Korea reactors unsuitable for developing weapons material in return for Pyongyang abandoning efforts to build an atomic bomb. North Korea has, however, now admitted it has built nuclear weapons, U.S. officials say.