Ukraine today appealed to Russia for a temporary ceasefire so repairs can be made to a power line to the Chernobyl nuclear power plant, warning there could be a radiation leak if the electricity outage continued.

Ukraine’s state-run nuclear company Energoatom said fighting between Ukrainian and Russian forces made it impossible to immediately repair the high-voltage power line to the plant, which has been captured by Russian forces.

Energoatom said radioactive substances could be released if...