The United States on Monday injected a note of caution into the mood of optimism surrounding recently revived talks on Iran’s contentious uranium enrichment program, calling on the Iranians to take “urgent, practical steps” to prove their sincerity in complying with obligations on the nonproliferation of nuclear weapons, The New York Times reported Tuesday, May 8. The European Union was more direct, asking Iran to suspend the enrichment, a step that Iran has said it will never take. Positive statements on all sides after the first round of resumed negotiations last month in Istanbul had helped to ease rising tensions. But the American and European statements, made at an international nonproliferation conference in Vienna, seemed to suggest that the atmosphere of good will in seeking to resolve the dispute diplomatically may have begun to fade.