A team of UN nuclear inspectors returned Thursday from a visit to a previously secret Iranian uranium enrichment site and their leader expressed satisfaction with the mission.
What the inspectors saw - and how freely they were allowed to work - will be key in deciding whether six world powers engaging Iran in efforts to reduce fears that it seeks to make nuclear weapons seek a new round of talks with Teheran.
"We had a good trip," said Herman Nackaerts, who headed the International Atomic Energy Agency inspection team.
Nackaerts said the nuclear agency planned to analyze the data from the visit, adding that IAEA head Mohamed ElBaradei would "then report in due time" on the results.
The Fordo site is near the holy city of Qom. Iran revealed it was building it September 21 in a confidential letter to the International Atomic Energy Agency. Just days later, the leaders of the US, Britain and France condemned Teheran for having kept it secret.
The West believes Iran revealed the site's existence only because it had learned that the US and its allies were about to make it public. Iran denies that.
The team's findings will be presented as part of a report to the IAEA's 35-nation governing board. Beyond that, ElBaradei is expected to brief the six countries - the US, Russia, China, Britain, France and Germany - attempting to persuade Iran to freeze enrichment.
The visit was the first independent look inside the enrichment plant, a former ammunition dump burrowed into the treeless hills south of Teheran. The inspectors were expected to have studied plant blueprints, interviewed workers and taken soil samples before wrapping up the mission.
Iran's other enrichment plant - a sprawling underground facility at Natanz - is already under IAEA monitoring. But its general refusal to heed UN Security Council demands and freeze enrichment has resulted in three sets of Council sanctions.
While the Islamic Republic insists it is enriching only to create fuel for a future nuclear reactor network, the international community is concerned because the material could be further enriched to weapons-grade uranium, used to arm nuclear warheads.
Along with the IAEA briefing on Fordo, the six powers are also awaiting another development later in the day or Friday that will go into determining whether they follow up on talks with Teheran early this month. By Friday, the Islamic Republic has promised to reveal whether it accepts a plan that would have it ship out 70 percent of its enriched uranium to Russia for further enrichment.
The West said that Iran agreed in principle to do so at the October 1 talks in Geneva, tentatively accepting a proposal that would see Russia enrich the exported material further for use in Teheran's research reactor.
The plan would commit Iran to turn over more than 1,200 kilograms of low-enriched uranium - more than the commonly accepted amount of low-enriched uranium needed to produce weapons-grade uranium.
Sending such a large amount out would thus temporarily get rid of most of the material Teheran would need to make a bomb.
But if Teheran did accept the plan in Geneva, it has subsequently backtracked.
Ahead of announcing its formal decision it has indicated that may insist that it be allowed either to buy the fuel for the Teheran reactor from abroad - or to ship the material in small batches. That would not reduce fears about further enrichment to weapons-grade uranium because Iran would be able to quickly replace small amounts it sent out of the country with newly enriched material.