Iran stepped up its defiance of international sanctions aimed at rolling back its nuclear program, vowing on Friday to continue enriching uranium and announcing it has produced and stored more of the gas used as a feedstock for enrichment.

Hard-line President Mahmoud Ahmadinejad said Iran would not give into U.N. Security Council demands that it suspend enrichment, state-run television reported.

"Iran will stand up to coercion. ... All Iranians stand united to defend their nuclear rights," state-run TV quoted Ahmadinejad as saying.

"Enemies have assumed that they can prevent the progress of the Iranian nation through psychological war and issuing resolutions, but they will be defeated," Ahmadinejad was quoted as saying on state-run TV.

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Iran has condemned as "invalid" and "illegal" a Security Council resolution passed last month that imposes sanctions against the Islamic Republic for refusing to halt enrichment.

The resolution orders all countries to ban the supply of specified materials and technology that could contribute to Iran's nuclear and missile programs. It also imposes an asset freeze on key companies and individuals in the country's nuclear and missile programs named on a U.N. list.

If Iran refuses to comply within 60 days, the resolution warns Tehran that the council will adopt further nonmilitary sanctions.

The United States and its allies accuse Tehran of secretly trying to produce atomic weapons, but Iran says its nuclear program is solely for peaceful purposes including generating electricity.

Ahmadinejad's comments came as China's President Hu Jintao urged Iran to give a "serious response" to the resolution, Chinese state media reported.

The resolution "reflects the shared concerns of the international community over the Iranian nuclear issue, and we hope Iran could make a serious response to the resolution," Hu said in his meeting with Iran's visiting top nuclear negotiator Ali Larijani, according to Xinhua News Agency.

But in another show of defiance, Vice President Gholamreza Aghazadeh, who also heads the Atomic Energy Organization of Iran, announced that Iran has produced and stored 250 tons of uranium hexaflouride gas, the feedstock for enrichment, state-run TV reported.

The hexaflouride gas, or UF-6, is being stored in underground tunnels at a nuclear facility in Isfahan to protect it from any possible attack.

"Today, we have produced more than 250 tons of UF-6. Should you visit Isfahan, you will see we have constructed tunnels that are almost unique in the world," state-run TV quoted Aghazadeh as saying.

The central Iranian cities of Isfahan and Natanz house the heart of the country's nuclear program. In Isfahan, a conversion facility reprocesses raw uranium, known as yellowcake, into uranium hexaflouride gas. The gas is then taken to Natanz and fed into the centrifuges for enrichment.

Iran has said it is moving toward large-scale uranium enrichment involving 3,000 centrifuges and says it plans to later expand this to 54,000 centrifuges.

Centrifuges spin uranium gas into enriched material, which at low levels is used to produce nuclear fuel to generate electricity. But further enrichment makes it suitable for use in building nuclear weapons.

Aghazadeh confirmed in April 2006 that Iran has produced 110 tons of uranium hexaflouride gas. Experts say that amount would be enough to produce up to 20 nuclear bombs if Iran was to divert its civilian nuclear program into making weapons.