Fears are growing over damage from Russian shelling to Ukraine's Zaporizhzhia nuclear power plant and from purported Russian plans to redirect power from the plant to Russian-annexed Crimea.
Russian forces have occupied the nuclear plant, the largest in Europe, since early March.
Ukrainian President Volodymyr Zelenskyy has meanwhile pledged to win back Crimea, one day after several explosions hit a Russian airbase on the annexed peninsula and killed at least one person. Ukrainian officials have not claimed responsibility for the attack.