Iran Stockpiling Nuclear Materials

The UN inspection that Iran is steadily stocking up on nuclear materials. Iran claims that they are obtaining these materials for "peaceful pourposes," but i believe that they are using them for weapons. This artical explains that it would take Iran a year for them to develop a bomb. But this makes me wonder, what will the US do to take precautions? Should they start preparing us for a situations like this? Will they warn us?