The inspectors had been due to arrive in Tehran on 28 September, but Iran delayed their visit until 1 October. The agency has expressed serious concern about Iran's attempts to enrich uranium for fuel in its proposed Bushehr nuclear power plant and about traces of weapons-grade uranium discovered at a facility this summer.

If Iran fails to prove its programme is entirely peaceful, the IAEA will report the matter to the UN Security Council. The US and Europe have strongly overlapping views on the need to make Iran's nuclear programme more transparent but diverge on how to persuade it to open up.

In Iran the IAEA demands are seen as evidence of US pressure. Iran insists the international community recognise its right to develop nuclear power and give it technical assistance.