Ukrainian President Volodymyr Zelenskyy said on Tuesday that Russia fired North Korean missiles in an overnight attack that killed six and wounded 19 in the southeastern city of Zaporizhzhia.

"The city was struck with North Korean ballistic missiles, Zircons, and guided aerial bombs," he said, referring to Russia's hypersonic cruise missile system, Zircon.

Zelenskyy had warned on Monday evening that Russia was preparing to station more North Korean troops on its territory and had already received more ballistic missiles from Pyongyang.

He has repeatedly sounded the alarm over deepening military ties between Moscow and Pyongyang, often while appealing for more Western air-defence supplies.

"This is the first time they cannot wage war without supplements from North Korea," he said in his nightly address, referring to Russian forces.