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Iran rebuffed a request by the U.N. nuclear agency chief in talks Thursday that it suspend uranium enrichment, and President Mahmoud Ahmadinejad insisted his country will not retreat "one iota."

The chief, Mohamed ElBaradei, looked much less optimistic after the four hours of talks with Iran's top nuclear negotiator, Ali Larijani, than he had when he arrived for the one-day visit and said the time was "ripe" for a political solution to the standoff.

ElBaradei, who is hoping to head off a confrontation between Tehran and the Security Council, put forward the U.N. request for Iran to suspend enrichment until questions over its nuclear program are resolved.

But Larijani indicated suspension was not an option. "Such proposals are not very important ones," he told reporters matter-of-factly while standing next to ElBaradei at a joint news conference after the talks.

Hours earlier, Ahmadinejad said enrichment was a line in the sand from which the Iranians would not retreat.

"We won't hold talks with anyone about the right of the Iranian nation (to enrich uranium), and no one has the right to retreat, even one iota," Ahmadinejad was quoted as saying by the official Islamic Republic News Agency.

"Our answer to those who are angry about Iran achieving the full nuclear fuel cycle is just one phrase. We say: 'Be angry at us and die of this anger,"' Ahmadinejad said.

Iran says its nuclear work is solely for peaceful, civilian purposes, but the U.S. and a number of its allies believe it is after a nuclear arsenal.

ElBaradei said the extent of Iran's nuclear program was uncertain: "We have not seen diversion of nuclear material for weapons purposes, but the picture is still hazy and not very clear."

During the 20 years of Iran's nuclear program, "lots of activities went unreported," ElBaradei said.

Higher-level enrichment makes uranium suitable for a nuclear bomb, though Western experts familiar with Iran's program say the country is far from producing weapons-grade uranium.

ElBaradei said that in their talks, Larijani had renewed Iran's commitment "to provide clarity to outstanding issues before I write my report to the (International Atomic Energy Agency) board by the end of this month."

The Security Council has given Iran until April 28 to cease enrichment of uranium. But Iran has rejected the demand and announced Tuesday that, for the first time, it had enriched uranium with 164 centrifuges — a step toward large-scale production.

Representatives of the five permanent Security Council members — the United States, Britain, France, China and Russia — discussed the latest development Thursday morning. The U.S. and Europe are pressing for sanctions, a step Russia and China have so far opposed.

"We want to see what the outcome of the discussions between ElBaradei and the Iranian government is. And when we get information on that, we'll consider what to do next," U.S. Ambassador to the United Nations, John Bolton, said after the meeting.

Secretary of State Condoleezza Rice said there will "have to be some consequence" for Iran's refusal to suspend uranium enrichment activities.

"There is no doubt that Iran continues to defy the will of the international community despite the fact that the international community very clearly said stop," Rice said.

Undersecretary for Arms Control Robert Joseph rejected Iran's claims that its nuclear program was for peaceful purposes, saying its enrichment "is for a weapons program and that is what we are trying to deal with."

"If it had nuclear weapons, I am sure (Iran) would be even more ambitious in its use of terror to undercut the prospects of peace in the Middle East," Joseph told reporters in Cairo, Egypt.

China said Thursday it was sending its assistant foreign minister to Tehran to convey its concerns about Iran's nuclear program.

Iran's deputy nuclear chief, Mohammad Saeedi, said Wednesday that Iran intends to move toward large-scale uranium enrichment involving 3,000 centrifuges by late 2006, and then expand the program to 54,000 centrifuges.

Saeedi said the 54,000 centrifuges would produce enough enriched uranium to fuel a 1,000-megawatt reactor, such as the one Iran has built with Russian assistance at Bushehr. The reactor is due to come on stream later this year.

Iran's nuclear chief, Gholamreza Aghazadeh, said Wednesday that Iran is prepared to give the West a share of Iran's enrichment facilities to allay fears that the country may divert some product to build weapons.

"The best way to get out of this issue is for countries that have concern to become our partners in Natanz in management, production and technology," he said, referring to the site of Iran's enrichment plant.

"This is a very important confidence-building measure," he said.