Iran has allowed UN 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 programme.

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 US, Britain, France and Germany are expected to urge Russia and China in talks on September 2 to consider a fourth round of UN 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. But the diplomat added it was still unclear whether Tehran’s concessions were a one-off.