A projectile landed within the plant's compound on Tuesday night, Iran's atomic energy organisation said, accusing the United States and Israel of being responsible.

Russia partially constructed the plant on Iran's Gulf coast and its technicians help operate it.

"We are deeply outraged by this reckless and irresponsible manifestation of a destructive course of action," the Russian foreign ministry said in a statement.

"It appears that the aggressors are deliberately seeking to provoke a large-scale nuclear disaster in the region," the ministry added.

Russia's atomic energy agency announced earlier that it was evacuating staff from the plant for safety reasons.

"Today, at approximately 7:20 am Moscow time (0420 GMT), 163 people left Bushehr for the Iranian-Armenian border," Rosatom CEO Alexey Likhachev was quoted as saying by the state RIA news agency.

"Right now, about 300 remain... Some people will stay. I think it will be a few dozen people who will oversee the equipment," he added in comments to reporters, including AFP.

Rosatom had already withdrawn 150 people working at the plant, amid the threat of US and Israeli airstrikes.

Before the conflict began, Russia was in the process of building two new reactors at the plant.

The UN's nuclear watchdog issued a statement on Tuesday calling for "maximum restraint to avoid nuclear safety risks".