South Korea scrambled fighter jets Tuesday to warn Chinese and Russian warplanes that had entered its air defense zone. But the warplanes did not fly into South Korea’s territorial airspace.

The Air Defense Identification Zone, which surrounds the territorial airspace of each country, is recognized so countries may demand foreign aircraft take steps to identify themselves to avoid misunderstandings.

The Joint Chiefs of Staff said four Chinese military aircraft flew in the morning near Ieodo, a submerged rock to the south of the peninsula that carries a weather research station. Two of them made their way out of the zone through the East Sea between South Korea and Japan.

Meanwhile 15 Russian military aircraft flew from north and over the East Sea. They flew back and forth into the zone over the East Sea before heading northeast, according to the JCS.

The JCS said China and Russia might have been holding joint drills, adding that Beijing had informed Seoul in advance of the exercises. The JCS said it was still looking into the event.

By Choi Si-young (siyoungchoi@heraldcorp.com)