A Russian air attack cut power to more than 1 million Kyiv residents and impacted substations carrying power from Ukraine’s atomic plants on Tuesday, prompting Ukraine to warn that Moscow is using the risk of nuclear disaster as a tool of coercion.

Moscow has stepped up a winter campaign against Ukraine’s battered ​energy system while grinding forward on the battlefield, as Kyiv faces U.S. pressure to secure peace after nearly four years of war, amid scant ‍signs the ⁠Kremlin wants to stop fighting.

Drone and missile strikes killed four people — three in the southeastern city of Zaporizhzhia and ‍one in the Kyiv region surrounding the capital. Other regions in the east, south and north of Ukraine also came under attack.