Kyiv and other cities across Ukraine were facing a major military assault by Russian forces overnight, in what Ukrainian Foreign Minister Dmytro Kuleba described as "a full-scale invasion."

The big picture: Shortly after Russian President Vladimir Putin announced a "special military operation" in Ukraine, Kuleba tweeted: "Peaceful Ukrainian cities are under strikes.

This is a war of aggression." President Biden said the U.S. would impose further "severe sanctions" on Russia in response.

Ukrainian security forces accompany a wounded man after an airstrike hit an apartment complex in Chuhuiv, Kharkiv Oblast, Ukraine, on Feb. 24. Photo: Wolfgang Schwan/Anadolu Agency via Getty Images

Tanks of Ukrainian forces move following Russia's military operation on Feb. 24, in Chuhuiv, Kharkiv Oblast, Ukraine. Photo: Wolfgang Schwan/Anadolu Agency via Getty Images

People react standing behind the cordoned-off area around the remains of a shell in Kyiv on Feb. 24. Photo: Sergei Supinsky/AFP via Getty Images

Police and security personnel inspect the remains of a shell in a street in Kyiv on Feb. 24. Photo: Sergei Supinsky/AFP via Getty Images

A man walks in a street as black smoke rises from a military airport in Chuguyev near Kharkiv on Feb. 24. Photo: Aris Messinis/AFP via Getty Images

A police officer stands guard by the remains of a shell in Kyiv on Feb. 24. Photo: Sergei Supinsky/AFP via Getty Images