A team from the United Nations nuclear watchdog has arrived in Iran - a day after issuing a confidential report accusing Tehran of failing to meet its obligations under the nuclear non-proliferation treaty (NPT).
Iran denies developing nuclear weapons
The report by the International Atomic Energy Agency (IAEA) says Tehran has not reported banned nuclear activities - but adds that it is taking steps to rectify this.
The document - leaked to the media - has been handed over to the IAEA's board of governors, who are to discuss the issue later this month.
But the Iranian official in charge of the country's nuclear energy programme, Khalil Musavi, has denied the allegations contained in the report.
Mr Musavi said Iran had not violated the NPT - the IAEA visit would show Iran's "transparent nuclear policy".
Iran insists it wants to use nuclear energy only for peaceful purposes and denies suggestions that it is developing nuclear weapons.
But it has so far declined to sign agreements that would allow tougher international inspections of its nuclear facilities.
The IAEA report accuses Iran of failing to meet its obligations to:
account for nuclear material
report its subsequent processing and use
declare facilities where the material is stored and processed
First nuclear plant comes online by summer 2004
Has signed up to the
Nuclear Weapons Non-Proliferation Treaty
Can now supply its own power stations with nuclear fuel
""This report ...shows the transparent interactions between Iran's atomic energy organisation and the IAEA, ," Mr Musavi said.
"We will study and evaluate this report and express our official stance in a declaration at the IAEA meeting on 16 June in Vienna."
"We will continue our co-operation with the agency," Mr Musavi said.
Iran forms part of what the United States calls the "axis of evil".
Washington has described the IAEA report as "deeply troubling", but Mr Musavi rejected the US reaction as "politically- motivated" propaganda.
Following US pressure, Russia - Iran's main partner in its nuclear power programme - has called on Tehran to sign an additional protocol to the NPT.
Relations between the IAEA and Iran have been good
That would permit tougher international inspections, giving the Iranians a chance to prove they are not trying to produce nuclear weapons.
But Iran has refused to agree to this until international sanctions are lifted and the country is given the technology to develop atomic energy for peaceful purposes.