The International Atomic Energy Agency last week accused Iran of denying its inspectors access in January to two sites.

The IAEA "should maintain its credibility and not follow up on any empty claims made by someone or some regime," foreign ministry spokesman Abbas Mousavi said.

"Questions must be based on a legal and technical case and not some regimes' political games as Iran does not consider this right or constructive," he added.

IAEA chief Rafael Grossi on Monday urged Iran to provide access to the two sites, and said it had failed to engage "in substantive discussions" to clarify its questions.

Diplomats say these were related to past projects of the 2000s that were alleged to have had a military dimension, and not to its current activities.

Iran's representative Kazem Gharib Abadi, said last week that Tehran had no obligation to grant the 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".

Iran's arch enemy Israel has claimed that its intelligence services have new information on the alleged past projects.

The back and forth comes with a landmark 2015 nuclear agreement between Iran and world powers hanging by a thread.

The accord -- offering Tehran sanctions relief in exchange for limits on its nuclear activities -- has faltered since the US withdrew from it in 2018 and began reimposing unilateral sanctions on Iran.

In retaliation Iran has progressively abandoned some of the limits set by the accord.

Other parities to the deal -- Britain, China, France, Germany and Russia -- have expressed continued commitment to the deal.

But so far they have been unable to make up for the United States in providing Iran with the economic benefits set out in the accord.