On Tuesday South Korea's Defense Ministry reported that the military fired warning shots after Russian planes entered national airspace.
Three Russian military aircraft entered South Korea's air defense identification zone off its east coast before one of them entered the country's territorial sky, according to the Defense Ministry.
South Korean jets then scrambled to the area to fire warning shots.
The Russian plane left, but later returned and again violated South Korean airspace, the ministry reported.
The Russian aircraft did not return fire.
The three Russian planes had entered the South Korean air defense identification zone with two Chinese military planes.
Before their flights with the Russians, the Chinese planes entered South Korea's air defense identification zone off its southwest coast earlier Tuesday, according to the South Korean official.
Chinese planes have occasionally entered South Korea's air defense identification zone in recent years.
Both the Russian and Chinese embassy officials in Seoul are to be summoned by the defense ministry later on Tuesday to register formal protests.