UN nuclear experts have inspected Iran's Arak heavy water plant for the first time since summer 2011, amid international concern that the half-built site may have a military purpose.
The one-day inspection of the site 240km southwest of Tehran was carried out by two experts, led by the head of the International Atomic Energy Agency's Iran task force, Massimo Aparo, but no details were immediately available.
The visit forms part of a mid-November agreement in Tehran that also allows the IAEA access to another nuclear-related site, as the Vienna-based agency seeks to clarify concerns about Iran's past nuclear activities.
The two IAEA inspectors arrived on Saturday and went straight into talks with Iranian nuclear officials.
After the meeting, Iran's Atomic Energy Organisation spokesman Behrouz Kamalvandi said Tehran had provided IAEA with "required information on ongoing research" about its new generation of centrifuges that enrich uranium by spinning it at supersonic speed.
Iran's nuclear work has for years been at the heart of disputes between Tehran and world powers, which suspect it of masking military objectives despite repeated denials.
A small heavy water research reactor at the Arak site is of concern because Tehran could theoretically extract weapons-grade plutonium from its spent fuel if it also builds a reprocessing facility.
The reactor has been plagued by a series of delays, however, and its stated completion date of 2014 is expected to slip back even further.
But a year after it eventually comes on line, it could provide Iran with an alternative to highly enriched uranium for use in a nuclear bomb.
Tehran insists its activities are entirely peaceful and says the Arak reactor would create isotopes for medical and agricultural use.
The IAEA does not have a permanent presence in Iran, but it regularly checks work on the Arak reactor, while also pushing Tehran to disclose any new design detail on the reactor since 2006.
Shashank Joshi, a research fellow at the London-based Royal United Services Institute, said that while the IAEA inspection of the heavy water plant - a first since August 2011 - was a "positive step," it was not a major development.
The plant "is not at the crux of Western concerns about Arak. In fact, inspections in general are not the central issue at Arak - the issue is over whether it will be activated or not, and how soon," he said.
