The fourth stage would see IAEA certification of there no longer being any undisclosed nuclear activities and agreement over the parameters of Iran's civil nuclear needs.

ECONOMIST: Iran and nuclear weapons

"Russia will have the right to opt out of the treaty if qualitative and quantitative parameters of the U.S. strategic missile defense begin to significantly effect the efficiency of Russian strategic nuclear forces, " Mr. Lavrov told the AP.

WSJ: U.S. Keeps First-Strike Nuclear Strategy