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.

Civilians pay heavy price as war in Lebanon drives death, displacement, UN says
Afghan Taliban says 400 killed in Pakistan air strike on Kabul hospital
Bomb attacks kill at least 23 in Nigeria's Maiduguri
Five countries warn against major Israeli ground offensive in Lebanon
Fire breaks out at Qatar's industrial area after missile interception
