Putin, who was speaking at a news conference in Vietnam, was reacting to a report from Yonhap news earlier on Thursday which said South Korea would review the possibility of supplying weapons to Ukraine after Putin and North Korean leader Kim Jong-un signed a mutual defence pact a day earlier.

Also read: Putin and Kim sign mutual defence pact

Putin said Seoul had nothing to worry about when it came to the pact between Moscow and North Korea.

"South Korea, the Republic of Korea has nothing to worry about because our military assistance under the treaty we signed only arises if aggression is carried out against one of the signatories. As far as I know, the Republic of Korea is not planning aggression against the DPRK (North Korea," Putin told reporters.

Also read: Putin warns Russia could hand other countries weapons to attack West

He warned Seoul against moving to supply weapons to Kyiv.

"As for the supply of lethal weapons to the war zone in Ukraine, that would be a very big mistake," he said.

"I hope that this will not happen. And if it does happen, then we will also take appropriate decisions, which are unlikely to please the current leadership of South Korea," said Putin.

The Russian leader was speaking to reporters in Vietnam at the end of a two-day trip to Asia. He held talks in North Korea a day earlier.