South Korea says it fired warning shots after Russian military planes entered its airspace.
Fighter jets were also scrambled in response.
According to the Defence Ministry in Seoul, it's the first time an aircraft from Moscow has violated the country's territorial sky.
It is planning to summon officials from the Russian Embassy to register formal protests.

Zambia steps up Ebola screening as neighbouring Congo sees cases rise
Pentagon chief says US ready to restart strikes on Iran if no deal
Myanmar's junta chief turned president heads to India
Three Latvian climbers die in fall from Mount McKinley in Alaska
Chain-reaction bus crash on Virginia highway kills 5 people
