Russia says six world powers concerned about Iran's nuclear program want Tehran to suspend uranium enrichment while negotiations are under way.

Russian Foreign Minister Sergei Lavrov said Saturday that it is necessary to explain to Iran what benefits Tehran would receive if it agreed to talks.

Lavrov was speaking in Moscow after meeting in London Friday with his counterparts from the United States, Britain, France, Germany and China.

He said the six nations did not discuss imposing new sanctions on Iran, but they did agree to improve a package of incentives first offered to Iran in 2006.

Iran's Foreign Minister Manouchehr Mottaki told reporters in Tehran Saturday that he has warned world powers not to cross Iran's "red lines."

In the past, Tehran has described the suspension of uranium enrichment as a "red line."

The six nations have been using a mix of incentives and sanctions to try to persuade Iran to halt its enrichment program.

Western nations suspect Iran is developing nuclear weapons, a charge Iran denies.

The U.N. Security Council has passed three resolutions sanctioning Iran for refusing to stop its controversial nuclear work.

Russia has relatively close ties with Iran and has taken a softer approach on sanctions than the United States. Washington doubts Iran will accept the incentives and prefers instead to push for the full implementation of the sanctions.

Without directly commenting on the nuclear standoff, Iran's state news agency, IRNA, reports that Supreme Leader Ayatollah Ali Khamenei said world powers have not succeeded in what he described as their efforts to deal a blow to Iran.

He made the remark in a speech to university students and professors in Shiraz, Iran, Saturday.

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