LONDON — The head of the United Nations nuclear regulatory body urged Iran on Monday to permit access by international inspectors to a military site near Tehran to ascertain whether tests have been carried out there on nuclear bomb triggers.

Yukiya Amano, the head of the International Atomic Energy Agency, was speaking at the body’s headquarters as its board of governors began a routine meeting just weeks after I.A.E.A. inspectors returned from talks in Tehran that failed to obtain access to the Parchin site, 20 miles south of Tehran.

“I request Iran once again to provide access to the Parchin site without further delay,” Mr. Amano said. “Providing access to the Parchin site would be a positive step which would help to demonstrate Iran’s willingness to engage with the agency on the substance of our concerns.”

The talks about Parchin are separate from the negotiations Iran is conducting with six global powers on the broader question of its disputed nuclear program, which Tehran says is for peaceful purposes. Western powers suspect that Iran is seeking the technology for nuclear weapons.