The attack on a nuclear power plant by Russia is "suicidal" and risks sparking a devastating disaster, the UN has warned.
United Nations Secretary-General Antonio Guterres has called on inspectors to be given access to a nuclear plant after the "suicidal" attacks.
The Zaporizhzhia nuclear power station was hit by shelling over the weekend, but is reported to be operating "in normal mode" according to Russian occupiers.
Ukraine and Moscow have blamed each other for the dangerous attacks on the plant and Ukrainian President Volodymyr Zelensky called it "Russian nuclear terror".
Russia accused Ukraine of blasting the site with a rocket launcher, hitting administrative buildings nearby.
Rafael Grossi, Director General of the International Atomic Energy Agency (IAEA), said: "I'm extremely concerned by the shelling at Europe’s largest nuclear power plant, which underlines the very real risk of a nuclear disaster that could threaten public health and the environment in Ukraine and beyond."
Zaporizhzhia is the largest nuclear facility in Europe and there is 855 tons of reactor core fuel said to be "highly vulnerable."
Grossi added: "Military action jeopardising the safety and security of the Zaporizhzhia nuclear power plant is completely unacceptable and must be avoided at all costs.
"What is at stake is extremely serious and extremely grave and dangerous. Every principle of nuclear safety has been violated.
"You have a catalogue of things that should never be happening in any nuclear facility."
Damage to nuclear power plants has the potential to be catastrophic and worries were heightened when invading Russian forces captured Zaporizhzhia in March, though it is still operated by Ukrainians.
On Friday, shells reportedly hit a high-voltage power line causing its operators to disconnect a reactor despite no radioactive leak being detected.
Guterres said: "We fully support the IAEA in all their efforts in relation to creating the conditions of stabilisation of the plant."
Zaporizhzhia is located in Southeastern Ukraine, currently under the occupation of Russian forces. Ukraine is expected to launch a major offensive to retake the area.
James Acton, co-director of the Nuclear Policy Program of the Carnegie Endowment for International Peace, told MSNBC that a failure of all the systems that keep a nuclear power plant safe has more chance of failing in a war.
He said on the Rachel Maddow Show:" Under normal conditions, an accident and nuclear power plant is very unlikely because you have all of these different safety systems in place.
"So you have an electricity grid connection to provide energy for the cooling, at multiple electricity connections. If they fail, you have emergency backup diesel generators.
"The problem is, in a war, a failure of all of these different systems together becomes much more likely... One could imagine damage to that plant or fire or damage to a power supplier cooling system that led to a serious accident."
