NEW YORK -- Iran's military complex at Parchin is classified by the United States as a legitimate military site run by a sovereign nation, used for conventional military purposes, the State Department said on Thursday.The statement, by department spokesman John Kirby, was a departure from past US characterizations of the controversial site, which has been shut off to international nuclear inspectors since 2006. The United Nations' International Atomic Energy Agency suspects Iran used the site in the past to experiment with nuclear weapons technology. Any site that hosts such activity— whether it be military or civilian, declared or undeclared by a member state of the Nuclear Non-Proliferation Treaty to the IAEA— counts as a nuclear site in the eyes of the UN nuclear watchdog. That includes sites that host experimentation with fissile material, as well as those that do not, but instead experiment with nuclear weapons technology such as trigger mechanisms."It’s important to remember that when you’re talking about a site like Parchin, you’re talking about a conventional military site, not a nuclear site," Kirby said on Thursday. "So there wouldn’t be any IAEA or other restrictions on new construction at that site were they to occur."Kirby was responding to reports of construction activity at the Parchin site. Based on satellite imagery, the IAEA believes Iran is adding an additional facility to the complex.Tehran says it does not need the IAEA's permission to build or adapt military facilities.For over a decade, the IAEA has sought answers to a set list of questions regarding the possible military dimensions of Iran's past nuclear work. The agency agreed on a "road-map" with Iran last month toward that end and hopes to conclude its inquiry by the end of the year.Theoretically, the inquiry is intended to conclude whether the site is conventional or nuclear in nature.If the investigation concludes to the satisfaction of the IAEA, Iran will begin receiving its sanctions relief, and the broader Joint Comprehensive Plan of Action— the formal name for the Iran nuclear deal— will go into effect.