Iran's supreme leader says his country will not stop work on its controversial nuclear program.

State television quoted Ayatollah Ali Khamenei as saying young Iranian scientists have guaranteed Iran's long-term energy security with their successes in nuclear science. He said a retreat would mean a complete loss.

His comments Sunday came as Russia's national security chief, Igor Ivanov, met in Tehran with Iran's top nuclear negotiator, Ali Larijani.

Media reports say Ivanov called for diplomacy as the way to end the standoff over Iran's nuclear activities. He said Moscow opposes any use of force against Tehran.

Ivanov's two-day visit to Tehran will include talks on economic incentives to be offered to Iran if it stops enriching uranium.

The five permanent members of the U.N. Security Council - the U.S., Britain, France, China and Russia plus Germany, have been working on a package of incentives to try to persuade Iran to stop enriching uranium. The group is also considering punitive measures in case incentives fail.

The United States has publicly said it is not interested in negotiating directly with Iran. But a report in the New York Times Saturday said U.S. Secretary of State Condoleezza Rice is discussing with top aides the possibility of direct contacts with Tehran.

The U.S. and Europe believe Iran is secretly developing nuclear weapons. Tehran says its nuclear program is only for peaceful purposes.

Some information for this report was provided by AFP and Reuters.