Iran and the United Nations’ nuclear watchdog are still negotiating over how to implement a deal struck last year to expand inspections of the Islamic Republic’s rapidly advancing atomic program, officials said Tuesday. The acknowledgment by the International Atomic Energy Agency’s leader Rafael Mariano Grossi shows the challenges his inspectors face, years after the collapse of Tehran’s nuclear deal with world powers and amidst wider tensions gripping the Mideast over the ongoing Israel-Hamas war.