Iran is "forever" banned from building a nuclear ****** under an existing international treaty, top US diplomat John Kerry said Wednesday, seeking to dismiss fears that limits on its program imposed in a new deal may eventually be lifted. "Please understand, there is ** reduction (of restrictions) at any time that permits Iran to build a nuclear ******," Kerry told US lawmakers when pressed whether a deal with Tehran would eventually allow them to develop atomic arms. "Iran is forever forbidden from building a nuclear ******, that is the nature of membership in the **n-Proliferation Treaty which they are a member of." Iran is a signatory of the nuclear NPT, but has already been found in **n-compliance with the global treaty, including for failing to declare its uranium enrichment program.