A senior United Nations nuclear agency team will visit Tehran later this month, with Iran saying it is ready to discuss allegations that it was involved in secret nuclear weapons work.
For more than three years, the Iranians have blocked International Atomic Energy Agency (IAEA) attempts to follow up on allegations from the United States and other Western powers, dismissing the charges as baseless and insisting that all of its nuclear activities are peaceful.
Even a decision to enter a discussion over the allegations would be a major departure from outright refusal to talk about them – and create hopes of future progress in the investigation.
Iran has accused the US of complicity in a series of assassinations of its nuclear experts – the latest being on Wednesday, when scientist Mostafa Ahmadi Roshan was killed by a bomb attached to his car by a passing cyclist.
Tehran has called on the UN to condemn the killing and two earlier attacks that left two nuclear scientists dead and another seriously injured.
The US Secretary of State, Hillary Clinton, denied any US role in the murder.