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.

Three killed in Russian strikes in Kyiv region, official says
Spain to establish border controls against Italy amid migration dispute
Thai teen kills 7 in rampage at home and school before shooting himself
US appeals court blocks Trump’s $400 million White House ballroom project
Spain dismantles one of Mediterranean's largest human smuggling networks
