KYIV, Ukraine — Ukrainian authorities issued air raid alerts for most of the country on Monday, after Russian strikes killed at least six people in the south of the country.

"Attention! Missile danger throughout Ukraine! MiG-31K takeoff," Ukraine's air force said in a post on Telegram confirming Russian bombers were airborne.

Russian air strikes earlier killed at least six people in southern Ukraine, a day after Moscow and Kyiv launched record overnight drone attacks on each other.

Five people were killed in the southern city of Mykolaiv, according to the regional governor, while a sixth died in Zaporizhzhia in an attack that authorities said wounded more than a dozen.

"Five dead," Mykolaiv Governor Vitaly Kim said early Monday on Telegram, revising up an earlier toll of four after an attack that set several residential buildings on fire.

About 300 kilometres  to the east in Zaporizhzhia, Ukraine's state emergency services agency said Russia carried out three air strikes that killed a man and damaged multiple buildings.

Zaporizhzhia Governor Ivan Fedorov said that 18 people were wounded, including five children.

"Boys aged 4, 16 and 17 and girls aged 15 and 17 have received the necessary medical assistance," he said on Telegram.

Overnight Saturday into Sunday, Russia fired 145 drones at Ukraine, according to Ukrainian President Volodymyr Zelensky, more than any previous single nighttime attack during the conflict.

Russia also said it had downed 34 Ukrainian drones targeting Moscow on Sunday, the largest attempted attack on the capital since the start of the war in 2022.