Russia fired its biggest-ever drone barrage on Ukraine on Monday, Kyiv said, escalating a deadly air campaign that analysts say offers little military value and instead appears intended to erode civilians’ morale.

The Ukrainian capital Kyiv and other regions came under a massive Russian drone-and-missile attack Sunday that killed at least 12 people and injured dozens.

Russia launched over 900 drones at Ukraine over the weekend and comes after U.S.-led efforts last week to reach a ceasefire between the two countries.