United Nations Secretary-General Antonio Guterres said on Monday that the risk of nuclear confrontation had returned after decades, calling on nuclear states to commit to no first use of the weapons.

Any attack on a nuclear plant is a “suicidal thing”, Guterres said, responding to reports of renewed Russian shelling of the Zaporizhzhia facility in Ukraine, Europe’s largest nuclear power plant.

Guterres spoke at a news conference in Tokyo after attending the Hiroshima Peace Memorial Ceremony on Saturday to commemorate the 77th anniversary of the world’s first atomic bombing.

He also called on Japan to halt public and private financing of coal projects as part of the country’s commitments in curbing fossil fuel emissions.