Key elements of a landmark nuclear agreement between Iran and six world powers were falling into place Sunday, but U.S. Secretary of State John Kerry warned there were important sticking points that may yet scuttle the deal. Mr. Kerry said the Obama administration could walk away from the negotiations if Iran proves “intransigent” on the remaining issues by Tuesday. That is the new deadline for a comprehensive agreement aimed at blocking Iran’s ability to move swiftly toward nuclear weapons in exchange for easing tight international sanctions. Senior U.S. and Iranian officials said advances have been made on two of the thorniest issues: the pace of sanctions relief for Iran and a United Nations investigation into charges that Tehran has secretly developed nuclear weapons technologies in recent decades. European Union foreign-policy chief Federica Mogherini said late Sunday that a final agreement, which has taken more than a decade of diplomacy, […]