Russian officials have said they would approve sanctions on Iran only if they saw hard evidence that Tehran's nuclear programme was not peaceful.
The US and some other major powers believe Iran may be building a nuclear bomb.
They say evidence that Iran is not complying with the United Nations Atomic Energy Agency is enough on its own to justify sanctions.
Up to now, Russia has said it is not convinced that sanctions on Iran to persuade it to abandon its uranium enrichment programme would work.
But Moscow has not before been explicit about the level of evidence it would need to consider sanctions.
