Both Russia and North Korea have denied that Pyongyang's weapons are being used in Ukraine.
Kim's powerful sister Kim Yo Jong last month accused Seoul and Washington of “misleading public opinion” on the issue.
– North Korean shells –
However, Ukraine has reported finding North Korean shells on the battlefield.
In May, South Korea said its northern rival had fired several short-range ballistic missiles. Some experts said they may have been tests of weapons used against Ukraine.
As the Kremlin and Pyongyang have publicly deepened their ties, Moscow's relations with pro-Ukrainian South Korea have become increasingly strained.
Seoul is a major exporter of arms to Kiev. Its President Yoon Suk-yeol pledged continued support in a phone call with Ukrainian President Volodymyr Zelensky last month.
South Korea last month announced separate sanctions on Russian and North Korean individuals and companies allegedly trading in military supplies.
Russia detained a South Korean man, Baek Won-soon, earlier this year on charges of espionage. He is believed to be the first South Korean detained in Russia on espionage charges in decades.
According to media reports, he was possibly a missionary who was helping North Korean workers in Russia escape the country.