"Russian military planes' KADIZ entry will not help efforts to stabilize the Korean Peninsula as well as Northeast Asia," Park told Falileev, according to the ministry. "Since there is also a possibility of mid-air collision, we request Russia to recognize the seriousness of this issue and look for measures to prevent such incidents from happening again."

Meanwhile, the Ministry of Foreign Affairs said its director-general for European Affairs Jung Ki-hong summoned Maxim Volkov, the No. 2 diplomat at the Russian Embassy to Korea, and expressed regret over the KADIZ violation.

Seoul's Joint Chiefs of Staff said Friday that two Russian military planes violated the KADIZ four times and flew away following warnings.

Russian aircrafts have entered the KADIZ several times this year, but this was the first time that they had breached it four times in one day, a JCS official was quoted as saying on condition of anonymity.

Meanwhile, Russia's defense ministry said two TU-95 bombers conducted a regular flight over the international waters of the East Sea, the Yellow Sea and a part of the Pacific Ocean.

The Russian ministry said the bombers were escorted by Korean and Japanese fighter jets on some parts of the flight. (Yonhap)