Noam Chomsky sums it up:
The basic point was explained very candidly by Henry Kissinger. He was
asked by the Washington Post why he now claims that Iran does not need
nuclear energy so it must be working on building a bomb, while in the
1970s he insisted forcefully that Iran needs nuclear energy and the
U.S. must provide the shah with the means to develop it. His answer was
pure Kissinger: "They were an allied country" so they needed nuclear
energy. Now they are not an ally, so they do not need nuclear energy.