Since Iran, for all we know, has not yet decided to actually build a nuclear device, there is plenty of time for another round of sanctions to bite. My suggestion: The Security Council should decide that any future supply of nuclear fuel to Iranian power/research plants (by Russians as in Bushehr, or others) should be paid for by an equivalent amount of Iranian Uranium, first enriched and then even raw. Iran does not have much Uranium, and is looking around even TODAY for a seller, so this exchange plan will bring an end to their enrichment program. Problem solved.
Obama says world must reach climate deal in Paris 'while we still can' (Reuters)
from the article: U.S., EU slam Iran nuclear enrichment activity at Security Council meet