The International Atomic Energy Agency (IAEA) and the UN Security Council will shortly receive a report on the latest contacts between the agency and Iran.
The UN nuclear watchdog has said Iran has provided it with information about its past nuclear activities as agreed under a work plan made in August.
Iran had agreed to give more details of its nuclear activities in an effort to forestall further economic sanctions.
But in a new report, the IAEA said it was continuing to check the completeness of Iran's declaration.
But this report effectively marks the start of a new effort by Western powers to restrain Iran's nuclear programme.
The IAEA also said Iran had also not suspended its uranium enrichment work as demanded by the UN Security Council and was operating 3,000 centrifuges.
It will be the basis of talks due to be held by the Security Council next week on whether to impose further sanctions.
The report could help determine whether world powers impose new UN sanctions.
On Tuesday, diplomats said Iran had given the IAEA a document containing design information that could be used for parts of a nuclear weapon. The IAEA had been asking Iran for the document since 2005.
Grindingly familiar
The latest confidential report from IAEA Director-General Mohamed ElBaradei looks set to mark the start of a new phase in international efforts to persuade Iran to curtail its nuclear activities.
The verdict of the report is likely to be mixed - some signs of progress and co-operation; some areas where still much more information is needed.
Iran says its nuclear programme is only for peaceful purposes
This inevitably leaves national governments free to interpret the report as they wish.
Some will see the glass as half-full, while Iran's critics will see it as being half-empty.
The IAEA report, along with another assessment from the EU's foreign policy chief, Javier Solana, will form the basis for deliberations when representatives of the five permanent members of the UN Security Council, along with Germany, meet on Monday in Brussels.
There, the US, UK and France will argue strongly for additional UN sanctions against Tehran.
Russia and China may well argue equally strongly to let Mr ElBaradei pursue the IAEA's efforts to extract more information from Iran.
For the US and the key European players, information on Iran's past activities is important but secondary to Tehran's basic failure to abide by the Security Council's demand that it halt its uranium enrichment programme immediately.
It all looks grindingly familiar.
The only new element is a marked shift in the French position - now much more critical of Iran - a development that raises the possibility at least of tougher EU sanctions should efforts in the Security Council fail.
