Iran has begun releasing details of components it imported unofficially for its nuclear programme.
Tehran says its nuclear programme is for energy only
The country's envoy to the United Nations nuclear watchdog, the International Atomic Energy Agency, said it was supplying a list of parts supplied through third parties.
Iran is under intense pressure to convince the UN this month that it has no plans to produce nuclear weapons.
UN inspectors are also seeking the right to mount snap inspections - a demand which Tehran has been resisting.
The list now being supplied to the IAEA is meant to cover unofficial purchases connected with the nuclear programme, which Iran insists is for civilian purposes only.
"We have already given a list of imported parts that were bought through intermediaries, and we are in the process of finishing this list," envoy Ali Akbar Salehi said.
"These are items which were not bought officially - they were bought through intermediaries and it is not possible to trace intermediaries."
He said that, in addition to supplying the list, Iran would show IAEA inspectors where the components had been stored.
On previous, arranged inspections to Iranian facilities,
inspectors found traces of highly enriched uranium - sparking suspicions that the country was seeking to build a nuclear bomb.
However, Iran, which now largely relies on Russian technology for its nuclear programme, contends that the traces were contamination from parts supplied from abroad.
Iran has a 31 October deadline by which it is required to satisfy the IAEA that it is not seeking weapons.
In a resolution passed on 12 September, the UN watchdog also called for Iran to agree immediately to snap inspections by signing an additional protocol to the Nuclear Non-Proliferation Treaty.
Talks with the IAEA in Tehran last week ended with the Iranians optimistic about the outcome, although reports say that Iran is seeking to attach conditions before agreeing to snap inspections.
Mr Salehi said then that agreement had been reached on a plan of action to clarify the issues of concern to the agency and speed up co-operation.
The most senior IAEA official involved in the talks, Deputy Director General Pierre Goldschmidt, returned to Vienna, but other officials and tactical experts have stayed on.
However the IAEA itself made no comment on the talks.
If Iran fails to satisfy the UN's experts, the issue may be referred to the UN Security Council, which may consider sanctions.