The head of the United Nations’ nuclear watchdog warned Wednesday that a projectile strike near Iran’s Bushehr nuclear power plant risked crossing the "reddest line" of nuclear safety, as fighting between the U.S., Israel and Iran intensifies.

A direct hit on an operating nuclear reactor like Bushehr could trigger a severe radiological incident, even as a recent strike caused no apparent damage to the plant’s core systems, International Atomic Energy Agency Director General Rafael Grossi said. 

"An accident on an operating nuclear power plant would be something very, very serious," Grossi told Fox News Digital Wednesday. "This is the reddest line of all that you have in nuclear safety."

"The possibility of dispersion in the atmosphere of radioactivity is very high if you get to the core of the reactor," he added.

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A projectile struck part of the Bushehr nuclear power plant complex in recent days, according to the International Atomic Energy Agency, marking the closest known impact on an operating reactor since the conflict began. It remains unclear what caused the strike or who was responsible.

Grossi said the impact appears to have hit a smaller structure within the facility’s broader premises — possibly a laboratory or auxiliary building — and did not affect the reactor itself or cause any reported casualties.

He noted that nuclear power plants are large compounds that include administrative buildings and support infrastructure beyond the reactor itself, increasing the likelihood that a strike could hit the site without directly damaging the core.

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Grossi said the agency has not conducted an on-site inspection, noting that "independent" verification would require being physically present, but said available imagery suggests the damage is not significant.

But he stressed the risks would be far more severe if the reactor were struck.

Unlike other nuclear facilities, an operating reactor contains a live core undergoing nuclear fission, meaning a direct strike could release large amounts of radioactive material into the environment.

Grossi said there is broad international understanding that nuclear power plants should not be targeted during conflict, even as recent strikes have come dangerously close to sensitive nuclear infrastructure.

Iran blamed the United States and Israel for the strike, though the claim has not been independently verified. 

U.S. officials have not confirmed involvement, and Israel’s military said it was not aware of any such strike.