Two Russian TU-95MS bombers intruded into Korea's air defense identification zone over the East and South Seas during joint Korea-U.S. military exercises last week.
Two F-15K fighter jets were scrambled from an air base in Dageu on Aug. 21 when the two Russian bombers flew into the zone, a military spokesman said.
"We understand that they were flying on patrol," the spokesman added.
The air defense identification zone is not recognized by international treaties but set by individual nations as the boundary where foreign aircraft need to seek prior permission from the country that claims it.
In February, Russian aircraft also intruded into Korea's air defense zone during joint drills.
Last week, the Russian bombers also intruded into Japan's air defense zone. Two F-15J fighters of the Japanese Self-Defense Force were scrambled in response, a Japanese government spokesman said.
The TU-95MS has a range of 15,000 km and a maximum speed of 920 km/h and can carry nuclear weapons.