Two Chinese and four Russian military planes on Thursday entered South Korea's air defense zone without providing prior notice, prompting responsive measures by the South Korean military. The simultaneous intrusion marks the first occurrence of its kind since June this year.

The six aircraft entered the Korea Air Defense Identification Zone, or KADIZ, off its east coast between 11:53 a.m. and 12:10 p.m. local time, South Korea's Joint Chiefs of Staff said on the same day in a statement.

Following their 17-minute entry, the aircraft left the area without violating South Korea's territorial airspace.

"Our military had identified Chinese and Russian military aircraft before they entered into the KADIZ and took tactical measures, including scrambling air force fighter jets, to prepare for accidental situations," the JCS said.

A country's Air Defense Identification Zone, or ADIZ, extends beyond sovereign airspace under international law, but established international principles dictate that all aircraft operating within an ADIZ must adhere to standard notice and coordination procedures.

The JCS assessed that the intrusion into the KADIZ occurred Thursday, during which China and Russia conducted combined aerial exercises.

Since 2019, China and Russia have been jointly dispatching military aircraft into the KADIZ around 1-2 times a year, citing combined exercises as the pretext and without providing advance notice.

Military aircraft from both China and Russia previously entered the KADIZ simultaneously in May and November of last year. The latest concurrent intrusion into the KADIZ occurred in June of this year.

The South Korean government continues to protest and call for measures to prevent recurrence whenever there is an incursion into the KADIZ by Chinese and Russian military aircraft. Despite these efforts, violations of the KADIZ have continued.

"After the military aircraft left the KADIZ, we communicated directly with China through a hotline and protested against the entry into the KADIZ without prior notification," an official from JCS said.

But the South Korean military clarified that it was unable to communicate with Russia regarding the intrusion into the KADIZ, as both countries do not operate military-to-military hotlines.