Any ballistic missile becomes supersonic on reentry, even...

Any ballistic missile becomes supersonic on reentry, even Germany's V2. Their path is easily calculated and an intercept trajectory instantly calculated and an intercept missile despatched. Easy peasy.

There is no hard definition of hypersonic but it is generally agreed that it should fly at least Mach 5, under it's own power, be manoeuvrable in real time. A standard ballistic missile on reentry is no longer powered nor is it controllable, it goes where it was told to at launch.

One not so small problem is that generating that speed with engine thrust, not gravity on reentry prolly needs a SCRAM Jet, Another is that the missile generates it's own plasma force around itself that interferes with radio command and control. Another is that the warhead cannot be large or the missile would be too heavy to reach high speed. Used as anti-shipping, the massive kinetic energy, even without a large explosive head, will penetrate deep into the heart of the ship where the vitals are. Israel does not have an aircraft carrier to target.

Why do you assume Iran has solved these problems when the US can't?