Their small, revving motors sound like motorcycles in the sky. Over the weekend, they streaked into Ukraine by the hundreds.

The drones fired by Russia. along with missiles, appeared to carry a message. Moscow’s barrages are often timed for geopolitically significant moments and aimed at symbolic targets, Ukrainian and European officials and analysts say.

The goal is to strengthen Moscow’s hand in talks, analysts say, and so far the Kremlin has paid no cost in additional U.S. sanctions as it escalates its attacks.

The latest such assault came on Sunday, when a Russian ballistic missile punched a hole in the roof of Ukraine’s Cabinet of Ministers building, the Kremlin’s first strike on the governmental center of Kyiv in three and a half years of war. The strike set the upper three floors aflame, in what was part of the largest single volley of missiles and drones fired in the war.

The attack came just three days after European heads of state gathered in Paris to consider sending troops to Ukraine after a cease-fire or peace settlement. Their mission, in part, would be to protect the Ukrainian government. Russia’s barrage appeared to signal that such troops would be at risk.

“This is a clear sign that Putin is testing the world,” President Volodymyr Zelensky said of the attack, which he said appeared intended to gauge whether other nations “will accept it or put up with it.”