A missile struck a building just 200 metres from the reactor at Iran's Bushehr nuclear power plant on March 18, prompting Russia's Rosatom to condemn the attack and warn it could trigger a catastrophic nuclear incident.

Bushehr is the first nuclear power plant in Iran and the Middle East. Construction began in 1975 with German involvement before Russia took over the project. The first reactor was commissioned in 2013 with Rosatom's participation. A second phase involving two additional reactors was under construction but large-scale works have been halted since the war began.

The strike hit the plant's metrology building at 6.11pm local time, Rosatom Director General Alexei Likhachev said. No damage to the reactor or injuries to personnel were reported.

"Firing on operational nuclear energy facilities is a flagrant disregard for the key rules and principles of international security," Likhachev said.

The IAEA confirmed it had received no reports of damage to the plant or casualties. Director General Rafael Grossi "again calls for maximum restraint to prevent the risk of a nuclear accident," the agency said.

Around 3,000 staff work at the plant, including 700 Russians. Rosatom began evacuating personnel after the war started on February 28 and has removed 250 so far, but nearly 500 remain. A third evacuation phase is being prepared.

Likhachev warned that a direct hit on the reactor could have global consequences. The reactor contains nearly 300 tonnes of nuclear fuel. Radiation from an accident would threaten not only Iran but the wider Persian Gulf, the Caspian Sea, the Red Sea and the Mediterranean.

"A strike on the Bushehr nuclear plant could result in catastrophe," Likhachev said. "An operating station and a station under construction are too complex to simply walk away from. As long as it is possible, we will remain present and do everything to ensure Bushehr-1 operates normally."

Grossi said the IAEA's access to Iranian nuclear sites had been "very seriously curtailed" and the agency could not provide definitive evidence regarding alleged weapons development.

Russia has lodged a formal protest with Israel over earlier strikes near the Bushehr facility, citing risks to its personnel. Moscow said it had previously informed Israel of the location of Russian staff at the plant.