United Nations Secretary-General Antonio Guterres sounded the alarm after the Russian-controlled Zaporizhzhia Nuclear Power Station in Ukraine was damaged in an attack over the weekend.
Zaporizhzhia is the largest nuclear power plant in Europe and is twice the size of Chernobyl.
"Any attack [on] a nuclear plant is a suicidal thing," Guterres said. "I hope that these attacks will end."
Guterres called on both sides to let the International Atomic Energy Agency (IAEA) access the plant and asses any damage.
Russia and Ukraine have both blamed each other for the attack, which damaged a high-voltage power line and knocked out power for around 54,000 people.
Energoatom, Ukraine's national energy company, said one worker was injured in the attack, which also damaged several buildings and knocked one of the reactors offline.
The company also warned that three radiation monitoring sensors were damaged, which could impede the "timely detection and response in case of aggravation of the radiation situation or leakage of radiation from spent nuclear fuel casks are currently impossible."
"This time, a nuclear catastrophe was miraculously avoided, but miracles cannot last forever," Energoatom said.
Energoatom's chairman Petro Kotin said that one of the shells came within 60 feet of a storage area for processed fuel.
"If they had hit the containers with the processed fuel, it would be a radiation accident," he said.