"This territory belongs to our state and such actions are unacceptable," the text of the protest said, as quoted by Kyodo news agency.
The South Korean Joint Chiefs of Staff said earlier in the day that a Russian A-50 control aircraft had illegally crossed into South Korean airspace twice over the Sea of Japan, and that South Korean F-16 fighters fired warning shots in response.
According to media reports, the incident took place several hours after two Russian Tu-95MS strategic bombers and two Chinese aircraft entered the South Korean air defence identification zone.
The Russian Defense Ministry refuted Seoul's claims, stressing that the South Korean fighters had performed non-professional manoeuvres and crossed course with the Russian planes, jeopardizing their security. The ministry made no mention of any A-50 aircraft.
The Russian Defense Ministry accused South Korea of repeatedly trying to impede Russia's flights over the Sea of Japan’s/East Sea's neutral waters, referring to an "air defence identification zone" unilaterally imposed by Seoul that is not envisaged in international regulations or recognized by Russia.
The Liancourt Rocks islands, also known as Dokdo by South Korea and Takeshima by Japan, have been administered by Seoul since 1954, a claim Japan disputes. Tokyo has suggested that Seoul should present the issue to the International Court of Justice. However, South Korea believes there is no dispute over the islands and considers them to be its territory historically, geographically and legally.