Iran's refusal to comply with UN demands that it suspend uranium enrichment activities some fear could produce nuclear weapons is set to feature high on the agenda when world leaders gather in New York next week for the UN General Assembly.

US officials have for weeks been expressing strong confidence that the permanent Security Council members -- Britain, China, France, Russia and the United States -- will swiftly reach agreement on political and economic sanctions designed to force Tehran to abandon its enrichment programme.

Such sanctions were called for in a Security Council resolution adopted in July, which gave Iran until August 31 to freeze its enrichment activity -- a demand Tehran ignored.

But with some Security Council partners increasingly reticent to go down the path of sanctions, State Department spokesman Sean McCormack admitted Thursday that the upcoming negotiations would be "hard-fought".

"The reality of it is that there are going to be intense negotiations on this," he said.