Officials say Moscow and Washington are nearing agreement on a formula that bridges differences over U.S. demands to quickly re-impose U.N. sanctions if Iran violates its commitments under a nuclear deal.

Washington sees a "snap-back" mechanism that allows previously lifted sanctions to be quickly reinstated as a cornerstone of any agreement. But Russia opposes any automatic sanctions triggers.

The two officials, who demanded anonymity because they were not allowed to discuss the confidential negotiations, declined to go into details.

Comments by France's ambassador to Washington Tuesday hinted at the possible compromise being worked on. He suggested that any "snap-back" would be subject to a majority U.N. Security Council vote.

That would satisfy Russian demands for a Security Council vote — even if it deviates from its normal consensus rules.