Large-scale Russian drone strikes on Sunday injured three civilians in Kyiv and at least two in Kharkiv, Ukraine’s second-largest city.

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.

With their dense mesh, the nets can tangle drone propellers. It’s a simple but effective countermeasure that reflects how low-tech means can blunt high-tech weapons in the war.