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 its questions, said its new chief Rafael Grossi.

"I hope in the next few days or hours we'll be able to unblock the current situation," he told a press conference after addressing the IAEA quarterly board of governors' meeting.

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 added that 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.

Iran's UN ambassador in Vienna, Kazem Gharib Abadi, said last week that Tehran had no obligation to grant IAEA access to sites if it deems the requests to be based on "fabricated information", accusing the US and Israel of trying to "exert pressure on the agency".

Israel has claimed that its intelligence services have new information on the alleged previous nuclear weapons programme in Iran.

Grossi told reporters Monday that the IAEA's requests for access were based on "concrete information" that had been validated.

"This is the agency information. Information can come from many sources. We have our own information... We never take any information at face value, never," he said.

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.

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.

Regarding the coronavirus epidemic, which has hit Iran, Grossi said inspection work in the country was continuing "without any problem".

The 2015 accord -- offering Tehran sanctions relief in exchange for restrictions on its nuclear activities -- has been faltering since the US withdrew from it in 2018 and re-imposed harsh sanctions on Iran.

This has prompted Tehran to progressively abandon the accord's restrictions since last year.

Other parties to the deal -- China, Britain, Germany, France and Russia -- have been meeting with Tehran to try to save the accord.