In December, Secretary of State Mike Pompeo announced that the Islamic Republic had tested a ballistic missile that could easily be equipped with a nuclear warhead. Last week, Pompeo warned Tehran to refrain from launching satellites with certain types of rockets since these use the same technology employed in ballistic missiles. Farzin Nadimi puts these remarks in context:
The [description of the missiles as given by Pompeo] in December match those of the Khoramshahr, a relatively new medium-range ballistic missile unveiled in September 2017 and test-fired on at least three occasions. . . . The Khoramshahr can reportedly carry a far heavier payload than would be required for a weapon whose purpose is pinpoint accuracy—its claimed 1,800-kilogram warhead would make it the largest in Iran’s arsenal. One possibility is that this extra capacity is designed to carry multiple warheads. . . . If Iran has in fact successfully tested such a capability for the first time, it would be an alarming milestone, since multiple warheads have a better chance of defeating missile defenses.
The Khoramshahr’s large payload would also make the job of mating it with a first-generation nuclear warhead relatively easy, at least in theory. One rule of thumb among experts is that any missile capable of carrying a 500–1,000-kilogram warhead can be mounted with a nuclear device. Khoramshahr reportedly offers twice that capacity—a troubling figure given the fact that miniaturizing a warhead is arguably one of the most daunting tasks in nuclear-weapons design.
[T]he international community should not forget that the [ballistic-missile] program remains a central pillar of Iran’s strategy for dominating the region. Although Tehran became less public about its missile advancements following the  nuclear deal, there has been no substantive halt in the program’s progress. Most troubling, the latest test indicates that [Tehran] is moving forward with the Khoramshahr, a ballistic-missile design that may already have the capability of lifting a heavy payload to targets anywhere in the Middle East or southern Europe.