Grossi, who is the director general of the UN agency, was greeted on Wednesday evening at the airport by Behrouz Kamalvandi, the spokesman for the Atomic Energy Organization of Iran or AEOI.

His visit to Iran comes a week after Donald Trump's election as the new US president. During his first term in the White House from 2017 to 2021, Trump was the architect of a policy called "maximum pressure" levying against Tehran biting sanctions that had been lifted through a landmark nuclear agreement in 2015.

Grossi is set to meet Thursday in Tehran with AEOI chief Mohammad Eslami as well as Foreign Minister Abbas Araghchi, who was chief negotiator in the nuclear talks between Tehran and the major powers that resulted in the 2015 deal formally called the Joint Comprehensive Plan of Action or JCPOA.

The deal, reached after 21 months of negotiations between Iran and world powers, gave Tehran sanctions relief in exchange for curbs on its nuclear programme to guarantee that it could not develop a nuclear weapon, something it has always denied wanting to do.

Three years later, then-president Trump unilaterally withdrew the United States from the agreement and reimposed heavy sanctions against Iran.

A year later, Iran reportedly started to gradually roll back its commitments to the nuclear deal, which only allowed Tehran to enrich uranium to 3.65 percent purity.

The IAEA says Iran has considerably increased its reserves of enriched uranium to 60 percent, close to the 90 percent needed to develop an atomic bomb.

"The one who left the agreement was not Iran, it was America," Iran's government spokeswoman Fatemeh Mohajerani said on Wednesday.

"Mr. Trump once tried the path of maximum pressure and saw that this path did not work."