VIENNA - Iran has allowed U.N. nuclear inspectors access to a reactor under construction after blocking visits for a year, and has let them upgrade monitoring at another site ahead of a crucial report on its atomic program.

Iran allowed International Atomic Energy Agency officials to inspect the site of the Arak heavy water reactor last week, diplomats said. The agency has been urging Iran to grant it access to verify it is for peaceful uses only.

Diplomats also said Iran had an upgrade to IAEA monitoring at the Natanz uranium enrichment plant. The IAEA is due to circulate its latest report on Iran next week.

The United States, Britain, France and Germany are expected to urge Russia and China in talks on September 2 to consider a fourth round of U.N. sanctions on Iran and the latest IAEA report will help form the basis for the discussions.

We must welcome every effort from Iran because we have been asking them to cooperate with the IAEA and they have not been doing so, one European diplomat said on condition of anonymity. But the diplomat added it was still unclear whether Tehran's concessions were a one-off.

Another diplomat questioned Iranian intentions. Look at it in context. Iran stonewalls for a year and then allows access right before the IAEA is to issue its report, the Western diplomat said.

Iran's IAEA envoy Ali Asghar Soltanieh was unavailable for comment. He was reported as saying on August 18 that Iran was ready for talks with the West on its nuclear program, but he later denied his comments.


Western hopes that Iran would negotiate a cap on its nuclear work faded when it crushed unrest over alleged fraud in a June election which returned Mahmoud Ahmadinejad to power.

But the new head of Iran's Atomic Energy Organization, Ali Akbar Salehi, appointed in July, is seen by analysts as a mild-mannered politician in favor of resolving Iran's nuclear row with the West through talks.

Salehi said last month the Islamic state and the West needed to renew efforts to build mutual trust and end a dispute over Tehran's nuclear program.

Iran, which says its nuclear program is peaceful, has said the Arak complex will be geared to producing isotopes for medical care and agriculture.

But Western powers fear Iran may configure the reactor to derive plutonium from spent fuel rods as an alternative source of bomb-grade fuel to its Natanz plant, which is under daily IAEA surveillance.

Inspectors have told the agency that containment and surveillance measures at Natanz, such as cameras and sealing, have been upgraded to the agency's current needs.

The IAEA said in June that the plant was swiftly outgrowing inspectors' ability to monitor it effectively -- namely, to verify that there were no deviations from civilian enrichment.

Some 5,000 centrifuges were enriching uranium then, with 2,400 more being set up on the same underground production floor. The next batch could be refining nuclear fuel full-time by now, with a similar number in line for installation.
(Additional reporting by Zahra Hosseinian in Tehran)