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.

Israeli strikes kill 8 people in Gaza, medics say
Thousands join Indian opposition protest demanding poll chief's resignation
Iranian negotiators continue talks in Doha aimed at ending conflict
Russian strikes cut power to thousands in Ukraine
