Russia pounded Kyiv with a massive missile and drone attack that killed four people, authorities said Sunday, after President Vladimir Putin threatened retaliation for strikes in Russian-occupied eastern Ukraine.

Multiple rounds of loud explosions were heard in the Ukrainian capital throughout the early hours of the morning, AFP journalists reported, in a barrage the air force said involved 600 drones and 90 missiles.

Kyiv Mayor Vitali Klitschko said two people had been killed in the capital and dozens wounded, while the head of the surrounding Kyiv region said two people had also been killed there.

Air defenses intercepted 549 of the drones and 55 missiles, the air force said. Ukraine's President Volodymyr Zelensky said the Russians had fired a nuclear-capable hypersonic Oreshnik missile in the barrage.

“Three Russian missiles against a water supply facility, a market burnt down, dozens of residential buildings damaged, several ordinary schools, and he [Putin] launched his ‘Oreshnik’ against Bila Tserkva [in central Ukraine],” Zelensky said on Telegram.