Iran has agreed to give inspectors from the International Atomic Energy Agency access to two suspected former nuclear sites.
A joint statement said Iran was doing so in good faith to resolve outstanding nuclear safeguards issues.
The agreement came during a visit to Tehran by the IAEA director general.
The global watchdog criticized Iran for not responding to questions about possible undeclared nuclear material and nuclear-related activities at the two sites and the blocking of inspections.
It is not known what the inspectors suspect may have happened at the sites. But the activities are believed to have taken place in the early 2000s.
This was long before Iran struck a historic deal with world powers that imposed limits on its nuclear program in return for the lifting of sanctions.