South Korea lodged a protest with Russia after its embassy in Seoul unfurled a large banner declaring “Victory will be ours,” an apparent reference to the anniversary of Moscow’s invasion of Ukraine.

The banner, written in Russian and displayed in red, white and blue, was seen over the weekend at the Russian Embassy and remained in place Monday. The fourth anniversary of Russia’s full-scale invasion of Ukraine falls Tuesday.

South Korea’s Foreign Ministry said it conveyed its position to Moscow, reiterating that it considers Russia’s invasion an illegal act. The ministry also cited recent public remarks by Russia’s ambassador.

Ties between Seoul and Moscow have deteriorated over Russia’s reported use of North Korean troops in the war. South Korea, which remains technically at war with North Korea, has condemned the deployments as a serious security threat.

According to South Korean and Western intelligence agencies, North Korea has sent thousands of troops to support Russia’s war effort. Seoul has estimated that about 2,000 have been killed.

Russia’s ambassador to South Korea, Georgy Zinoviev, was quoted by local media this month praising North Korean troops for helping retake parts of Russia’s Kursk region from Ukrainian forces.

Neither the Russian nor Ukrainian embassies in Seoul immediately commented.