A team from the UN nuclear watchdog arrived in Tehran today seeking details about Iran's offer to answer unresolved questions about its disputed nuclear programme.
Iran has offered to draw up an "action plan" to address suspicions its nuclear programme has military goals. Tehran insists its aims are purely civilian but faces the prospect of more UN sanctions for failing to convince world powers.
Olli Heinonen, deputy director of the UN International Atomic Energy Agency (IAEA), is heading the delegation which is expected to hold talks with Iran's chief nuclear negotiator Ali Larijani and his deputy Javad Vaeedi.
The United States and its European Union allies are considering whether Iran's offer of transparency is anything more than an exercise to buy time and avert further UN measures.
The UN Security Council has imposed two rounds of sanctions on Iran since December for failing to halt uranium enrichment, the part of Tehran's programme that most worries the West because it can make fuel for power plants or bomb material.
World powers are now considering a third round of sanctions. The IAEA wants explanations for traces of highly enriched - bomb-grade - uranium found on some equipment.
It also wants to know more about experiments with plutonium, the status of research into an advanced centrifuge able to enrich uranium three times as fast as the model Iran now uses, and documents showing how to cast uranium metal for a bomb core.
IAEA director Mohamed ElBaradei has said the Iranian offer of transparency combined with a slowdown in uranium enrichment work has raised hopes of defusing the row.