South Korea scrambled fighter jets on Thursday after at least six Chinese and Russian warplanes were seen enterering its air defence zone, the country’s Joint Chiefs of Staff (JCS) said.
Two Chinese and four Russian jets entered South Korea’s Air Defense Identification Zone (KADIZ) off its east coast on Thursday afternoon, beginning at 11.53am (2.53am GMT) and exiting by 12.10pm, the military said.
The JCS said the planes were detected before they entered the KADIZ and it mobilised the air force’s fighter jets in response, according to the Yonhap news agency.
The planes did not violate South Korea’s territorial airspace, the military said.
It is not the first time that Russian and Chinese planes have jointly entered South Korea’s air defence zone. Similar flights in 2019 led to a significant escalation of tensions with South Korean jets firing hundreds of warning shots towards the Russian and Chinese jets conducting joint exercises.
FIR is an ICAO concept relating to civil aviation. Military operations do not have to follow ICAO rules and FIR procedures, never mind request permission to enter a FIR zone in international airspace.
Even in regards to civilian aviation FIR airspace is not subject to the whims of the nation administering it (unless the airspace is also in their territorial airspace). Airlines can be banned for territorial airspaces not FIRs.
So no Incheon FIR is not internationally recognized as South Korea airspace.
Nor was the KADIZ set up to support Inceon FIR it was setup during the Korean war by USAF.
Having said that pretending to have an ADIZ is not illegal in itself as long as you do not take illegal actions in support of it. You can track planes via radar,ask them to identify themselves (they can ignore you) and even fly up to them in international airspace.
Though shooting even warning shots as they claimed they did in 2019 would be an illegal act of agression.