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.

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.

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.