The U.S. and Iran voiced caution over the prospect of a deal permanently curbing Tehran’s nuclear program on the eve of international talks. The diplomacy in Vienna, slated to last six months, follows an interim agreement in November between Tehran and global powers that froze parts of Iran’s nuclear program in exchange for an easing of Western sanctions. The new round of diplomacy aims to end what the West views as Iran’s pursuit of nuclear weapons. The Obama administration has outlined a negotiating position that calls for Tehran to drastically roll back its nuclear infrastructure to ensure it is solely for peaceful purposes. U.S. officials say this likely would have to include the dismantling or mothballing of thousands of centrifuge machines, which are used to produce nuclear fuel, and the shuttering or conversion of nuclear sites. Senior Iranian officials say they won’t accept any major curtailment of the program. […]