TEHRAN (Reuters) - An influential Iranian leader suggested on Monday Iran should quit the Non-Proliferation Treaty in protest against a U.N. censure over its nuclear activity, but its atomic energy chief dismissed such a move.

Tehran caused an international outcry on Sunday when it announced plans to build 10 more uranium enrichment sites in retaliation for a rebuke by the U.N. nuclear agency for covering up an enrichment project for at least two years.

Russia said it was “seriously concerned” by Iran’s gambit to massively expand enrichment, criticism that could raise Western hopes for Russian backing for harsher sanctions against Tehran.

Washington condemned the plans as a serious violation of U.N. Security Council resolutions.

Parliament speaker Ali Larijani said there was little point in Iran staying in the treaty if it was liable to be reprimanded by the International Atomic Energy Agency for exercising its right to develop peaceful nuclear energy.

“I believe that their moves are harming the NPT the most ... Now, whether you are a member of the NPT, or pull out of it, makes no difference,” Larijani told a news conference.

However, Ali Akbar Salehi, head of Iran’s atomic energy agency and seen as a relative moderate, told Reuters later Tehran had no wish to leave the NPT.

“Our spiritual leader says that to obtain nuclear weapons is a sin -- if we wanted to obtain nuclear weapons we would leave the Non-Proliferation Treaty,” he said through an interpreter.

“We are naturally enduring a lot of pressure but we will remain in the treaty.”

TENETS OF ISLAM

Iranian officials have previously said Iran had no intention of leaving the NPT, under which its nuclear sites are subject to IAEA inspections, or to use enrichment to produce fuel for nuclear weapons, which it says violate the tenets of Islam.

Analysts believe Iran would think twice before quitting the NPT since this would betray weapons ambitions and could provoke a pre-emptive attack by Israel and possibly the United States.

It could take Iran many years to equip and operate 10 new enrichment plants.

Iran dismissed skepticism voiced by some Western analysts about its ability to execute the plan. “They will see in the future that what we have said is no bluff,” First Vice-President Mohammad Reza Rahimi told Fars news agency.

If Iran expands enrichment as it says, suspicions that it plans to develop nuclear weapons will grow since it lacks the technology needed to convert low-enriched uranium (LEU) it is making into fuel for civilian nuclear power plants.

Such technology is not needed to refine LEU into the fissile material used for nuclear warheads.

Larijani said there was still room for diplomacy.

Iran's President Mahmoud Ahmadinejad greets people outside the presidential palace in La Paz November 24, 2009. Ahmadinejad is on a one-day visit to Bolivia. REUTERS/Pilar Olivares

Referring to the six world powers pressing Iran for steps to prove it does not seek nuclear weapons, he said: “It would be useful for them also to use this diplomatic opportunity to let Iran work in the framework of the IAEA and international supervision to assure them that Iran’s activities are peaceful.

“Of course they are free to choose another method and Iran will act accordingly.”

The IAEA board angered Iran when it censured it for covertly building a second uranium enrichment plant near the holy city of Qom, in addition to its main IAEA-monitored one at Natanz, and calling for a halt to construction.

“STRONG MESSAGE”

Salehi, quoted by state broadcaster IRIB, said the decision to go ahead with 10 new enrichment sites was spurred by the IAEA resolution, adding: “Iran’s government sent a strong message.”

Susan Rice, U.S. ambassador to the United Nations, said Iran’s plans were unacceptable and might lead to increased pressure on Tehran to comply with U.N. resolutions.

“We view the Iranian announcement, if it is in fact accurate and implemented, that they intend to build 10 additional facilities as completely inappropriate and further isolating Iran from the international community,” she told reporters.

Russia, which has so far refused publicly to support U.S. suggestions that broader economic sanctions may be needed to restrain Iran, said it was “seriously concerned by the latest statements of the Iranian leadership.”

France said Iran should be given a “last chance” in talks over its atomic program and it must heed IAEA warnings.

“The fact that Iran persists in ignoring the demands of a big independent agency like the IAEA, that’s very dangerous,” Foreign Minister Bernard Kouchner said.

Germany’s Foreign Minister Guido Westerwelle said Iran’s announcement “clearly goes in the wrong direction. Iran is urged to cooperate with the IAEA without ifs and buts ... It is clear that if Iran rejects the outstretched hand of the international community, it must expect further sanctions.”