The US has said it hopes Iran will still accept a confidence-building nuclear deal even as it plans to meet again with five other world powers to discuss steps to end Tehran's defiance.

Meeting in Brussels on Friday, the six powers expressed disappointment that Iran has not responded positively to a deal to ship low-grade nuclear fuel abroad or agreed to new talks. But US State Department deputy spokesman Robert Wood said that the United States and its negotiating partners Russia, China, Britain, France and Germany were not yet at the point of closing the window on dialogue.