Ukrainian President Volodymyr Zelenskiy said on Sunday that defence relationships with his country's partners would have to change in light of North Korean transfers of people as well as weapons to Russian forces in Ukraine.

The Kremlin on Thursday dismissed South Korean assertions that North Korea may have sent some military personnel to help Russia against Ukraine and might be weighing a bigger deployment.

"We see that the alliance between Russia and such regimes as the North Korean one is getting stronger," Zelenskiy said in his nightly video address. "This is not just about the transfer of weapons, this is in fact about the transfer of people from North Korea to the armed forces of the occupiers.

"It is obvious that under such conditions our relationship with our partners needs to evolve," he added. "The front line needs more support. We are talking about more long-range capabilities for Ukraine and more sustained supplies for our forces rather than a simple list of military hardware."

South Korea's Defence Minister Kim Yong-hyun said on Tuesday that "there was a high possibility" North Korea could deploy troops to help Russia in the war with Ukraine.

Kim also told a parliamentary hearing that news reports of North Korean military officers having been killed in a Ukrainian strike on territory controlled by Russian forces were likely true.

Kremlin spokesman Dmitry Peskov, asked on Thursday if North Korea was sending its troops to fight in Ukraine, told reporters: "This looks like another bit of fake news."