* IAEA suspects Iran worked on designing a nuclear bomb * Iran rejects accusations; Western officials want Iran to address questions by the International Atomic Energy Agency (IAEA) on allegations of past efforts to develop a nuclear ******* capability, something the country denies. They say Iran clarifying the IAEA's concerns would also influence a diplomatic push by six world powers to negotiate an end to a decade-old standoff over the Islamic Republic's nuclear programme, suggesting some sanctions relief may depend on it.