"The purpose of this outrageous attack was to cut off the Ukrainian people's access to heat and electricity during winter and to jeopardize the safety of its grid," Biden said in a statement.

"Let me be clear: the Ukrainian people deserve to live in peace and safety, and the United States and the international community must continue to stand with Ukraine until it triumphs over Russia's aggression."

The president said that the United States will "continue to work tirelessly" to back Ukraine against Russian forces in the ongoing war.

Ukraine's air force said that the early morning attack by Russia using 78 air and ground missiles and 106 Shahed drones damaged critical equipment in Ukraine's power grid, causing outages on Christmas Day.

Ukrainian President Volodymyr Zelenskyy decried the deliberate attack on Christmas day as "inhumane."

Ukraine shot down "more than 50 missiles and a significant number of drones" and was still hit as there are power outages in a number of regions as engineers are trying to restore power, Zelenskyy said.

"Russian evil will not break Ukraine and will not spoil Christmas," Zelenskyy said.

The strikes wounded at least six people in the northeastern city of Kharkiv and killed one in the region of Dnipropetrovsk, the governors there said.

Christmas in Ukraine, where most of its people are Christian Orthodox, used to be celebrated on Jan. 7, as is the case in Russia, but that changed in 2023 to Dec. 25, the date used in Western countries.

Nearly three years into the war, Washington has committed $175 billion in aid for Ukraine.

President-elect Donald Trump, who will take office on Jan. 20, has said he wants to bring the war to a swift end.

Trump's choice for special envoy to Ukraine and Russia, retired Lt. Gen. Keith Kellogg, has condemned the Christmas Day attack.