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Iran's supreme leader said Tuesday that Tehran's nuclear program was "irreversible" and warned that any retreat in the face of international pressure would "break the country's independence."

Ayatollah Ali Khamenei took the tough line over the nuclear program hours before the five permanent members of the U.N. Security Council were to hold discussions on what action to take if Iran doesn't back away from its atomic ambitions.

President Mahmoud Ahmadinejad also vowed to resist pressure from the U.N. Security Council over the program, which the United States says aims to produce nuclear weapons. Iran denies that charge, saying it wants only to generate nuclear energy.

Iran and the West appeared to be on a collision course Tuesday, as French President Jacques Chirac said that Europe cannot make "the slightest concession" to Tehran on preventing proliferation of nuclear arms. He said Europe does not contest Tehran's right to civilian nuclear energy.

Khamenei, who holds final say in all matters in Iran, ordered its diplomats abroad to defend the country's nuclear program, saying that backing down would force Tehran to gradually give up all its foreign policy goals.

"The Islamic Republic of Iran considers retreat over the nuclear issue ... as breaking the country's independence, which will impose huge costs on the Iranian nation," state television quoted Khamenei as saying to diplomats brought home from its embassies around the world for consultations with Iranian leaders.

"Any retreat at this point will bring an unending chain of pressures and further retreats. Therefore, this path is irreversible and the foreign policy establishment has to bravely defend Iran's right," he said.

In a nationally televised speech in northern Iran, Ahmadinejad said "no power" can take nuclear technology away from Iran.

"Rest assured that the technology to produce nuclear fuel today is in the hands of the youth of this land, and no power can take it back from us," Ahmadinejad told the crowd of thousands, who chanted, "Nuclear energy is our right."

The United States and its European allies want Iran to permanently abandon uranium enrichment, which can produce fuel for nuclear reactors or fissile materials for an atomic bomb.

The five permanent members of the U.N. Security Council — the United States, Russia, China, Britain and France — have been considering proposals to pressure Iran to resolve questions about its nuclear program, including demands that it abandon enrichment. The council has the power to impose sanctions but Russia and Chine oppose such a step.

China expressed optimism Tuesday that negotiations could still resolve the dispute, and called on Tehran to cooperate.

"Now there is still room to solve the Iranian nuclear issue through diplomatic negotiations," said Chinese Foreign Ministry spokesman Qin Gang. "We hope Iran can cooperate closely with the International Atomic Energy Agency and do more to build up mutual confidence to help reach a solution."

In Moscow, Russian negotiators held talks with an Iranian delegation and urged a diplomatic solution to the standoff. The Iranians left the Russian capital after the talks, with no announcement of any progress.

Moscow has been trying to convince Tehran to accept a U.S.-backed compromise proposal under which uranium enrichment for Iran's nuclear program would take place in Russia. But negotiations ended in a stalemate after Tehran rejected a Russian demand to suspend uranium enrichment activities at home.

Russian Foreign Minister Sergey Lavrov said Monday that Moscow was "very disappointed with the way Iran has been conducting itself in these negotiations."

"One day they reject it, the other day they don't," he said.

Ahmadinejad said pressure from Washington and its allies would not force Iran to abandon its drive to produce nuclear fuel.

"They should know that through propaganda, political pressures and games they play nowadays such as issuing statements, making angry gestures, (they) can't prevent the Iranian nation from pursuing its path," he said in his speech Tuesday.

The IAEA reported Iran to the U.N. Security Council last week after Tehran resumed nuclear research and small-scale uranium enrichment.

Iran has insisted it will never give up its right under the Nuclear Nonproliferation Treaty to enrich uranium and produce nuclear fuel. It restarted research-scale uranium enrichment last month, two years after voluntarily freezing the program during talks with Germany, Britain and France.

It also has threatened to start large-scale uranium enrichment if the council imposes any sanctions.