"The young Iranian engineers, with their successes, have guaranteed the long-term energy future of the country. We must not lose this at any price because any retreat would be a 100 percent loss," Khamenei was cited as saying.

Khamenei's remarks came as visiting Russian National Security Council chief Igor Ivanov was holding talks with senior Iranian officials on Tehran's controversial nuclear program.

"Unlike the U.S., Russia believes Iran's nuclear program needs to be resolved only through dialogue. Any use of force will further complicate the issue and will cause tension in the region," Ivanov said during a meeting with Iran's top nuclear negotiator Ali Larijani.

Arriving late Saturday night, Ivanov would also discuss with the Iranian side new proposals by the European Union trio of Germany, France and Britain which offer incentives if Tehran suspends uranium enrichment and possible sanctions if it continues.

Diplomats of the five permanent members of the UN Security Council plus Germany met in London on May 24 and discussed the new proposals of the EU trio but stopped short of making a final agreement.

Foreign ministers of the six nations are expected to hold more talks on the EU package late this week.

Washington has accused Tehran of secretly developing atomic weapons under a civilian front, a charge denied by Iran, which insists its nuclear program is fully peaceful.

Russia offered last year to produce nuclear fuel on Russians oil for Iran in a bid to ease fears that Iran would divert uranium into warheads.

Talks broke down when Iran insisted uranium enrichment had to be carried out on its territory.