Following Vladimir Putin's visit to North Korea yesterday, South Korea has just made a statement condemning a pact signed by the two pariah states.
Russia and North Korea agreed on a new defence deal vowing to help each other in case of invasion.
South Korea hit out at the pact, which it called "absurd", and said it would reconsider sending weapons to Ukraine.
The presidential office said Russia's military assistance to the North would have a negative impact on relations between Seoul and Moscow.
Any actions helping North Korea increase its military capability are a violation of UN resolutions, it said.
It added it would further strengthen South Korea's security cooperation with the US and Japan.
