Iran has agreed to give International Atomic Energy Agency inspectors access to two suspected former nuclear sites.
A joint statement said Iran was doing so in good faith to resolve outstanding issues related to nuclear safeguards.
The agreement came during a visit to Tehran by the IAEA’s director general.
The global watchdog has criticised Iran for not answering its questions about possible undeclared nuclear material and nuclear-related activities at the two locations and blocking inspections.
It is not clear what inspectors suspect might have happened at the sites. But it is thought the activities took place in the early 2000s.
That is long before Iran struck a landmark deal with world powers that placed limits on its nuclear programme in return for the lifting of sanctions.