The advance would be another step in achieving proficiency in the entire nuclear fuel cycle. Iran said in January that it had produced the first nuclear fuel rod, and that it had to find a way to make them because Western sanctions prohibit their purchase from foreign markets.

By compromising on the IAEA probe, Iranian negotiators in Baghdad could argue that the onus was now on the other side to show some flexibility and temper its demands. Although Amano's trip and the talks in Baghdad are formally separate, Iran hopes progress with the IAEA can boost its chances Wednesday in pressing the U.S. and Europe to roll back sanctions that have hit Iran's critical oil exports and blacklisted the country from international banking networks.

It was unclear, though, how far the results achieved by Amano would serve that purpose, with him returning without the two sides signing the deal, despite his upbeat comments.