Ukrainian forces fired more than 1,000 drones at Russia overnight, including hundreds that were launched toward Moscow, officials said Sunday, as the Kremlin was wrapping up the third and last day of its parliamentary elections.

Moscow’s mayor described the wave of drones as the “largest ever” drone attack on the Russian capital and said there had been damage to the Moscow Oil Refinery, which is among several sites that supply the Russian capital, and a residential building.

Across the wider Moscow region, the attack killed two people and wounded 20, local Gov. Andrei Vorobyov said. The dead were a 74-year-old man and a 44-year-old woman, he said.

Since Russia’s invasion more than four years ago, Ukraine has become a global leader in military drone technology, deploying domestically produced long-range drones alongside missiles for strikes deep inside Russia. Its drone technology has impressed governments and defense manufacturers around the world.

Kyiv is aiming to make the Russian public feel the war’s consequences and pressure Russian President Vladimir Putin into negotiating a peace settlement. Putin has so far shown no signs he intends to stop the invasion.

Instead, Moscow and Kyiv have been drawn into an escalating duel of long-range aerial strikes as fighting along the roughly 1,250-kilometer (780-mile) front line in eastern and southern Ukraine has slowed, restricted by large numbers of drones and ground robots threatening troop movements.