The appeal came as International Atomic Energy Agency officials renewed talks with Iranian envoys aimed at persuading Tehran to allow IAEA experts to visit a suspect site at the Parchin military complex.
The agency believes that site was used by Iran to test multipoint explosives of the type used to set off a nuclear charge. Iran denies such experiments and insists it has no plans to turn its civilian nuclear program to making weapons.
A computer-generated drawing obtained by The Associated Press from a country tracking Iran's nuclear program depicts a containment chamber that would be used for such work. The IAEA has not commented, but Olli Heinonen, who was the senior official in charge of the Iran file until he left the IAEA last year, says the drawing is "very similar" to a photo he has seen and identifies as that of the Iranian chamber, adding even the colors of the two images match.
IAEA Deputy Director General Herman Nackaerts said the agency was seeking Iran's cooperation, ahead of Monday's talks at Iran's mission to the IAEA and other Vienna-based U.N. organizations.
"We are here to continue our dialogue with Iran in a positive spirit," Nackaerts told reporters. "The aim of our two days (talks) is to reach an agreement on an approach to resolve all outstanding issues with Iran.
"In particular, clarification of the possible military dimensions remains our priority," Naeckerts said, adding: "It's important now that we can engage on the substance on these issues and that Iran let us access people, information, documents and sites."
The official who shared computer-generated drawing said it proves the chamber exists, despite Tehran's refusal to acknowledge it. He said it is based on information from a person who had seen the chamber at the Parchin military site, adding that going into detail would endanger the life of that informant.
The official comes from an IAEA member country that is severely critical of Iran's assertions that its nuclear activities are peaceful and asserts they are a springboard for making atomic arms.
Beyond IAEA hopes of progress, the two-day meeting is being closely watched by six powers trying to persuade Iran to make nuclear concessions aimed at reducing fears it may want to develop atomic arms as a mood-setter for May 23 talks between the six and Tehran in Baghdad.
Warnings by Israel that it may attack Iran's nuclear facilities eased after Iran and the six - the United States, Russia, China, Britain, France and Germany - met last month and agreed there was enough common will for the Baghdad round. But with the Jewish state saying it is determined to stop Iran before it develops the capacity to build nuclear weapons, failure at the Iraq talks could turn such threats into reality.
The IAEA has been blocked by Iran for more than four years in attempts to probe what it says is intelligence from member states strongly suggesting that Iran secretly worked on developing nuclear weapons. Iran says the suspicions are based on forged intelligence from the United States, Israel and others.