The NPT was based on a simple bargain. The existing nuclear powers pledged to make every effort to disarm themselves of nuclear weapons. Civilian nuclear technology was promised the developing world on condition that they observed the treaty and submit their programs to safeguards.
The United States and the West generally are not satisfied with that arrangement. They have come to the conclusion that the construction of a nuclear infrastructure provides a ready means to building a weapon, if the state so desires. It can stay within the rules until it decides to withdraw, after which there is no choice but to submit to another nuclear power or to go to war. This claim has been especially pressed against Iran and its nuclear program.
Iran has refused to budge. Despite impressive pressures and promises of rewards from European states, in which Russia and China have partially joined, Iran insists on its right to develop its own nuclear industry.