Due to Iran's refusal of stopping uranium activities, the United Nations Security council has made the resolution against Iran for three times. As reported, new resolution of sanctions against Iran will be made at the beginning of next month. The U.S. representative has made clear that the nuclear fuel exchange agreement was with the purpose of buying time.
The western countries all along believed that Iran planned to have its own nuclear weapons, therefore strongly urged stopping any uranium enrichment works.
Iran insists its rights of peaceful use of nuclear energy and control of nuclear technology, showing strong antagonist against the western countries. The mutually long-term hostility and suspicion is the major reason why the Iran issue hasn't been solved.