Ukraine’s capital, Kyiv, was rocked by a massive combined drone and missile assault on late Friday, sending residents scrambling for cover as explosions and bursts of machine gun fire echoed across the city into the early hours of Saturday.

The debris of intercepted missiles and drones fell in at least 4 city districts of the capital, acting head of Kyiv military administration, Tymur Tkachenko, wrote on Telegram. According to Tkachenko, six people required medical care after the attack, two fires sparked at Solomianskyi district of Kyiv.

The latest large-scale Russian attack came just hours after a rare moment of cooperation between the warring nations, as Ukraine and Russia conducted a significant prisoner exchange. Hundreds of soldiers and civilians were swapped in what officials described as the first phase of an agreement brokered during a meeting in Istanbul last week.

Prior to the attack, city mayor Vitalii Klitschko warned Kyiv residents of more than 20 Russian strike drones heading towards Kyiv.

President Volodymyr Zelenskyy said the first phase brought home 390 Ukrainians, with further releases expected over the weekend that will make it the largest swap of the war. Russia’s Defense Ministry said it received the same number from Ukraine, news agency Associated Press reported.

The exchange, which would be the latest of dozens of swaps since the war began and the biggest involving Ukrainian civilians at one time, didn’t herald any halt in fighting. Battles also continued along the roughly 1,000-kilometer (620-mile) front line, where tens of thousands of soldiers have been killed, and neither country has relented in its deep strikes, The Associated Press said.