"Our military first detected the unidentified flight in the southwest of Ieodo Island," the South Korean Joint Chiefs of Staff reported, according to the Yonhap news agency.
The aircraft was tentatively identified as either a Shaanxi Y-8, a typically unarmed transport aircraft, or an electronic warfare plane of unknown make. "We are still confirming the exact model," Seoul said.
Apparently, the Chinese aircraft entered their Korean Air Defense Identification Zone (KADIZ) at 9:30 a.m. before passing into Japan's air identification zone and finally returning to Chinese airspace at about 2:05 p.m.. Seoul responded by scrambling several fighters to conduct a sortie and "closely monitor" the aircraft.
Thus far, neither Beijing nor Tokyo have commented on the alleged incident.
Air defense identification zones like KADIZ are considered to be international airspace, so the Chinese plane did not violate South Korean territorial integrity. However, planes entering another nation's zone are expected — but not legally required — to report their route and purpose to the nation in question.
Ieodo Island, which is known as Suyan Rock in China, is not an island at all but actually a submerged rock, siting about 15 feet below sea level at low tide and sporting a small South Korean research station on a platform above the water. According to the United Nations Convention on the Law of the Sea, such a formation can not be claimed as territory by any country, but it is still disputed between the two Asian nations as they cannot agree whose economic zone it falls within.
In 2013, South Korea announced that the air over Ieodo Island was part of KADIZ. China de facto ceded the rock to the South at that time, when the Chinese Foreign Ministry stated they had "no dispute" with South Korea adding Ieodo Island to their air defense identification zone.
But relations between Seoul and Beijing have degraded over the sticking point of that other Korea: China has been the primary backer of Pyongyang for decades, while relations between the two Koreas have been frayed and tense, to say the least, since late 2016.
In December, five Chinese military aircraft entered the KADIZ, which Seoul described as an infringement. China rebutted that the flythrough was part of a routine operation.
Beijing-based military commentator Li Jie told the South China Morning Post that the exercise was an example of China flexing its muscles in the region, reminding South Korea and the other players that they're still a key component of the geopolitical situation on the Korean Peninsula.
"This is China stamping its sovereignty in the area," Li said. "China feels there is a lot of uncertainty regarding how South Korea is handling the nuclear problem, and also their joint military operations with the US after the Olympics," he said. "[Beijing] wants to show that it is highly concerned about these issues."