Iran and the United Nations nuclear watchdog agency have opened talks in Vienna about the Islamic republic's nuclear activities.
Speaking before the talks on May 14, the International Atomic Energy Agency's (IAEA) Deputy Director General Herman Nackaerts urged Iran to allow his team to visit a suspect military site at Parchin, where there are concerns that work toward nuclear weapons may have taken place.
The talks on May 14 lasted about five hours with neither side commenting. Discussions were set to resume on May 15.
The last such meeting, in February, failed to reach agreement.
The IAEA is investigating suspicions that Tehran may be seeking to develop a nuclear weapons capability.
Tehran denies any such plan.
Iran is due to discuss the nuclear issue with six world powers -- Britain, China, France, Russia and the United States and Germany -- in Baghdad on May 23.
The IAEA suspects a large containment chamber at Parchin could be used for possible nuclear-weapon development. Such suspicions were contained in a report on Iran's nuclear program issued by the IAEA in November.
IAEA head Yukiya Amano says the issue is a "priority" for his team of senior officials in this week's discussions.
Iran has rejected the accusations as fabricated but so far has not granted repeated requests by the UN agency to visit the site.
Tehran has repeatedly denied it is secretly working to build a nuclear weapon, something the West suspects, especially the United States and its close ally Israel.
Meanwhile, Iran has warned Western powers that applying pressure could jeopardize even more high-stake talks on its nuclear program.
Catherine Ashton, the European Union's foreign policy chief, said on May 11 she hoped the upcoming talks would form the basis for Iran to eventually abandon its "nuclear weapons program."
Based on AFP and Reuters reporting