Iranian and American officials ended a round of high-level nuclear talks here on Monday considering a proposal that would strictly limit for at least 10 years Iran ’s ability to produce nuclear material, but gradually ease restrictions on Tehran in the final years of a deal. A senior American official traveling with Secretary of State John Kerry and Energy Secretary Ernest J. Moniz said the United States would insist that Iran’s nuclear program be constrained for “at least a double-digit number of years” from being able to produce enough material for a bomb should it decide to “break out” of the accord. The United States has insisted that Iran’s breakout capacity be constrained for as long as possible from producing enough nuclear material to create a bomb in a year. Iranian officials have said they want an agreement that would allow their country to ramp up the […]