The director general of the U.N. nuclear watchdog, which is investigating whether Iran carried out work related to developing an atom bomb, visited a sensitive military site during a trip to the country, the agency said on Sunday.
The military site, called Parchin, has been at the centre of a debate over the level of access that the International Atomic Energy Agency (IAEA) will have in policing a deal reached in July between Iran and six world powers.
The IAEA is due to issue an assessment this year on "possible military dimensions" of Iran's nuclear programme under a roadmap agreement accompanying that deal. One open question is whether Iran carried out high-explosives testing at Parchin that could be related to making a nuclear warhead.
"The director general visited the site of Parchin, together with the head of the Department of Safeguards, Tero Varjoranta," the International Atomic Energy Agency said in a statement.
Western intelligence agencies have recognized Parchin as a potential chemical, explosives and munitions production site since the 1990s. Suspicions about possible nuclear arms-related research there came later, Western diplomats say.
Tehran denies conducting research related to nuclear weapons at Parchin or anywhere else in the country.
A spokeswoman for the IAEA declined to provide details on the visit to Parchin by the director general, Yukiya Amano. Iranian state media described it as ceremonial rather than an inspection of the sprawling site.
"Yukiya Amano visited the road construction near Parchin facilities," Behruz Kamalvandi, spokesman for the Atomic Energy Organization of Iran, was quoted as saying by state news agency IRNA.
IAEA access to Parchin, a facility the agency has not visited in a decade, was one of the most sensitive issues during negotiations that led to the July 14 deal between Iran and world powers, which provides for restrictions on Iranian nuclear activities in exchange for a lifting of sanctions.
Under that deal, Iran cannot receive its promised sanctions relief until it clears up outstanding IAEA questions about past research that Western powers suspect was related to the development of atomic weapons.