"Iran's development of a nuclear weapon, I believe is unacceptable," he said at a news conference in Chicago. "Iran's support of terrorist organizations, I think is something that has to cease," he said.
Obama said he would be reviewing a letter from Iran's President Mahmoud Ahmadinejad, congratulating him on his election, and would "respond appropriately." But he said the U.S. approach to Iran could not be done in a "knee-jerk" fashion. "I think we've got to think it through," he said.
