Eleven Chinese and Russian military aircraft entered South Korea’s air defense identification zone without notice Friday, prompting the South Korea’s Air Force to send its fighter jets to the scene.

According to the Joint Chiefs of Staff, five Chinese military planes and six Russian aircraft entered the KADIZ over the East and South Seas between 9:35 a.m. and 1:53 p.m. and exited it. They did not violate the country's airspace.

The JCS said it identified the Chinese and Russian military aircraft before they entered the KADIZ and deployed Air Force’s fighter jets and performed its usual tactical measures against potential accidental situation.

An air defense identification zone is not a country’s airspace but an area designated by a country for defense purposes, which foreign aircraft are expected to notify before entering under international norms.