At least three children were among 27 people wounded as a result of a Russian drone attack on Ukraine's second-largest city of Kharkiv overnight that damaged apartments and a kindergarten, Ukrainian authorities said on Monday.

Russia launched 550 drones and missiles across Ukraine overnight in the largest aerial assault since the war began. The capital Kyiv was the primary target.

Ukraine said it struck a Russian air base on Saturday, while Russia continued to attack Ukraine with hundreds of drones overnight as part of a stepped-up bombing campaign that has dashed hopes for a breakthrough in efforts to end the more than 3-year-old war.