The head of the UN's atomic watchdog on Monday (March 9th) urged Iran to "co-operate immediately and fully" with a landmark nuclear agreement with world powers that is hanging by a thread.
The International Atomic Energy Agency (IAEA) called on Iran to provide access to two locations, and said Tehran had failed to engage in "substantive discussions" to clarify the agency's questions, said agency chief Rafael Grossi.
Grossi said the IAEA had raised questions "related to possible undeclared nuclear material and nuclear-related activities at three locations that have not been declared by Iran".
He said the lack of access to two of the three sites and Iran's failure to engage in talks was "adversely affecting the agency's ability... to provide credible assurance of the absence of undeclared nuclear material and activities in Iran".
An IAEA report last week revealed that Tehran refused the agency access in January to the two sites.
Diplomats say these are related to Iran's alleged military nuclear projects in the 2000s, and not its current activities. But the renewed focus on Iran's historic programme could add to current tensions.
A second IAEA report last week outlined Iran's continued breaches of the terms of the 2015 nuclear accord, but did not report any restrictions in access to nuclear facilities.
Speaking at a quarterly meeting of IAEA's 35-member Board of Governors, Grossi said "to date, the agency has not observed any changes to Iran's implementation of its nuclear-related commitments" since January when Tehran announced it would cease all obligations.