The United States intends to move very quickly in early September to impose UN sanctions on Iran for refusing to suspend its enrichment of uranium, a senior State Department official said Thursday. "They will be well-deserved," Undersecretary of State Nicholas Burns told reporters. "It's not a mystery to the Iranians what is going to happen." The UN Security Council already has said Iran faced sanctions if it did not suspend uranium enrichment, a key step in making nuclear weapons. Iran has until the end of the month to respond officially. It also had said it would reply by next Tuesday to a proposal by the United States and the European Union for concessions that include US supply of some civilian nuclear energy.