Smoke billows from the site of a Russian strike on a shopping center in Kyiv, Ukraine, Sunday, amid the Russian invasion. EPA-Yonhap

KYIV, Ukraine — 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 defences intercepted 549 of the drones and 55 missiles, the air force said. Ukraine's President Volodymyr Zelensky said Russia had fired its nuclear-capable hypersonic Oreshnik missile and wounded 69 people in the capital in the barrage.