The drone attack on May 17 hit an electricity facility at the plant, risking potentially shutting it down -- a "serious situation indeed", Rafael Grossi said.

"From what we saw this was a very carefully targeted operation," Grossi told journalists in Abu Dhabi after visiting the Barakah plant.

The United Arab Emirates blamed militants in Iraq for the incident, which followed weeks of attacks by Iranian drones and missiles during the Middle East war.

"In spite of the fact that the Emirati professionals acted very quickly and could address the situation, (it could have taken) out the reactor because of the loss of external power," Grossi said.

"This means that whoever was behind this knew exactly what they were doing. This is of extreme gravity."

Grossi said he was also visiting the UAE's Gulf neighbours, who could be affected by any accident at the Arab world's only nuclear plant.

"I think this is pretty serious and this is why we have been very vocal," he told AFP in separate remarks.

"I've been to Kuwait, to Qatar, now here, and I'm heading to Riyadh because several countries in the region have serious concerns," he added.

Grossi said he would hold a special session of the IAEA's board of governors and that the body is providing technical expertise and support for the UAE.

The "worst-case scenario" would be a direct hit on Barakah or Iran's Bushehr plant -- which has also been targeted in the war -- with the potential for a leak of radioactive material, he told AFP.

Cutting the power "has the practical effect of... necessitating emergency generation to keep the safety functions of the plant running", he said.

"To get to a meltdown would take much, much more. We would be talking of a situation where you would completely run out of external power."

Hamad Al Kaabi, deputy chairman of the Board of Management of the Federal Authority for Nuclear Regulation, said Grossi's visit "reflects the international community view that an attack on such a plant is not acceptable".

He said Barakah, which has been fully operational since 2024, remains a "cornerstone" of energy infrastructure in the oil-rich country.

"Whether we expand (nuclear power) in the future is yet to be decided, but I think Barakah makes a compelling case," he told AFP.

"If anything, it's proved that these plants can be maintained safely and securely."