In a possible new bid to gain Iranian cooperation on allegations that it had a nuclear weapons program, the director-general of the International Atomic Energy Agency (IAEA), Yukiya Amano, says his organization will share sensitive data with Iran “when appropriate.”

Iran for years has complained that it has not seen the documents and other materials to back up IAEA and Western intelligence claims that it carried out a series of nuclear weapons-related studies in the late 1990s. According to a 2007 US National Intelligence Estimate, Iran halted a structured weapons program in 2003 but elements of the work may have continued.

Amano, speaking at the Council on Foreign Relations, appeared to be making a new pitch for Iranian cooperation in advance of a scheduled visit by an IAEA delegation to Iran next week, on Dec. 13. To provide “credible” assurances about its nuclear past, he said, it was not necessary for Iran to resolve “100%” of international concerns but to agree on a process and start down that path.

“Believe me, we are reasonable people,” he told a group of journalists after the event. “Credible doesn’t mean zero or 100% […] Bypassing these issues with a military dimension or refusing to respond to questions is not the solution.”