Iran is "forever" banned from building a nuclear weapon 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 no reduction (of restrictions) at any time that permits Iran to build a nuclear weapon," 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 weapon, that is the nature of membership in the Non-Proliferation Treaty which they are a member of."
Iran is a signatory of the nuclear NPT, but has already been found in non-compliance with the global treaty, including for failing to declare its uranium enrichment program.
World powers -- Britain, China, France, Germany, Russia and the United States -- appear to be close to nailing down a deal with Iran which would rein in its suspect nuclear program.
The aim is to construct a deal, which through limiting enrichment and destroying centrifuges for example, would ensure that it would take the Islamic Republic at least a year to gather together the fissile material to build a bomb. That would give the international community ample time to ward off the threat.
US officials have said they want the deal to remain in place for an amount of time spanning "double digits" but denied they were thinking of only 10 years.
At a hearing of the House Foreign Affairs Committee, Kerry was seeking to dismiss reports that after that time Iran would be free to develop atomic weapons.
But he stressed that "Iran has already mastered the fuel cycle" and insisted that the key was to ensure that its nuclear program "was exclusively for peaceful purposes" -- as allowed for under the NPT.
US and Iranian negotiators are due to meet again next week in Switzerland, and American officials have said Kerry could again join the talks as a March 31 deadline for a political framework on the Iran deal looms.
National Security Advisor Susan Rice said that any deal would be a "phased one."
Iran is "not going to be able to convince anybody on day one that they have stopped enrichment," she told PBS television late Tuesday.
"They're going to have to prove over time through their actions which will be validated that they are, in fact, upholding their commitments. So this will be a phased process any way you slice it."