KYIV (AFP) — Russia pounded Kyiv with a massive missile and drone attack that killed four people early on Sunday, authorities said, 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, Agence France-Presse (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 56 wounded, while the head of the surrounding Kyiv region said two people had also been killed there, and nine wounded.

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.

“They are genuinely deranged.”

The blasts in the capital caused a residential building near the government district to shake, while dozens of people took shelter in an underground metro station in the city center, AFP reporters said.

Residents were instructed to stay in shelters, as city officials warned fires had broken out.

Ukrainian authorities and the US embassy had earlier warned of a possible significant attack on Kyiv, after Russia said it would “punish” those responsible for deadly strikes in a part of eastern Ukraine under its control.

Klitschko said damage had been recorded in every district of Kyiv, adding that a strike on a school had sparked a fire and another on a business center led to people being trapped in a shelter.

Ukrainian authorities said Russian strikes had also wounded 11 in the Cherkasy region and seven in the Dnipropetrovsk region.