TEHRAN - Iran criticized on Monday U.S. President Barack Obama for saying Tehran posed a threat with its nuclear program and urged Washington and other countries possessing atom weapons to dismantle their arsenals.

Foreign Ministry spokesman Hassan Qashqavi made the comments a day after Obama, who is seeking to engage Iran diplomatically in a sharp policy shift from George W. Bush's approach, set out his vision for ridding the world of such arms.

Delivering a speech in Prague given new urgency by North Korea's rocket launch, Obama also said the United States would go ahead with plans to build a missile defense shield in Europe as long as Iran posed a threat with its nuclear activities.

Qashqavi noted that the Bush administration, which spearheaded a drive to isolate Iran over its disputed nuclear plans, had also described the Islamic state as a threat.

It seems that the repetition of the past U.S. administration's accusations (against Iran) would be in contrast with the slogan of change (by Obama), Qashqavi said.

And such a thing -- nuclear armament -- does not exist in Iran to be inferred as a threat, he said.

The West suspects Iran's nuclear program is a cover for developing bombs. Iran, the world's fourth-largest oil producer, says it is a peaceful drive to generate electricity.

Asked about North Korea's rocket launch, which analysts said was effectively a test of a ballistic missile designed to carry a warhead as far as the U.S. state of Alaska, Qashqavi said Iran's and North Korea's missile activities were not related.

Obama last month offered Iran a new beginning of diplomatic engagement, following three decades of hostility. Iran has responded cautiously to the overture, saying Washington must show real policy change toward Iran rather than in words.

Qashqavi said nuclear weapons had no place in Iran's defense doctrine and that the existence of such arms was a serious threat to the global community.

We, like the rest of the world community, are awaiting a world free of nuclear arms, Qashqavi said.

Our expectation from the U.S. and others is to take serious and practical measures toward nuclear disarmament and dismantling of weapons of mass destruction, he said.

Obama pledged on Sunday to cut the U.S. nuclear arsenal, to bring the Comprehensive Test Ban Treaty into force and to seek tough penalties for those that broke rules on non-proliferation.

He presented Iran with a clear choice of halting its nuclear and missile activity or facing increased isolation.

Tehran has repeatedly rejected international demands to stop its most sensitive atom work and officials say Iran will unveil good news when it marks its national nuclear day on Thursday.