VIENNA: The United States is unlikely to strike an agreement with Iran to save the 2015 Iran nuclear deal unless Tehran releases four U.S. citizens Washington says it is holding hostage, the lead U.S. nuclear negotiator told Reuters on Sunday.

The official, U.S. Special Envoy for Iran Robert Malley, repeated the long-held U.S. position that the issue of the four people held in Iran is separate from the nuclear negotiations. He moved a step closer, however, to saying that their release was a precondition for a nuclear agreement.