The UN atomic agency failed during talks in Tehran Wednesday to resolve long-standing questions over Iran's alleged past efforts to develop nuclear weapons, an Iranian official said.
"We discussed certain solutions to resolve the two outstanding questions, and it was decided to wind up the discussions at the next meeting," said Reza Najafi, Iran's ambassador to the International Atomic Energy Agency, quoted by ISNA news agency.
"We hope to reach this stage at the next session," he said without giving a date, at the end of a one-day visit by chief IAEA inspector Tero Varjoranta and a team of experts.
Iran had agreed to answer agency enquiries about alleged explosive testing and research into nuclear bomb making by last August.
Wednesday's meeting was the first since Iran and six major powers agreed on April 2 the main outlines of potentially historic deal curtailing Iran's nuclear activities in return for sanctions relief.
Western officials say it is crucial for Iran to answer the IAEA's questions about the "possible military dimensions" of its activities before any sanctions can be eased.
Iran rejects the allegations as false information provided the IAEA by the Islamic republic's enemies, complaining that Tehran has not even been given an opportunity to see much of the supposed evidence itself.
Under the April 2 agreement, Iran agreed to scale back dramatically its nuclear programme and submit to ultra-tight IAEA inspections in order to make any eventual dash to make a nuclear bomb extremely difficult and easily detectable.
The accord has a target date of June 30.