Chinese officials issued a radio warning to an American B1-B Lancer Bomber flying near South Korea on Sunday, claiming that the aircraft had illegally entered Chinese airspace and ordering them to leave.

The airspace in question is included in China’s Air Defense Identification Zone (ADIZ) over the East China Sea, a territory China officially claimed in 2013, but that America and its allies continue to identify as international airspace.  The particular region of the East China Sea the B1-B was flying over includes a chain of islands that has seen overlapping territorial claims levied by the Chinese, Japanese, and South Koreans.

According to China’s official policy, aircraft must notify China before entering into the contested region – a policy both American and Japanese aircraft do not recognize or honor.

“Pacific Air Forces … did not recognize the Chinese Air Defense Identification Zone (ADIZ) when it was announced in November of 2013, and does not recognize it today,” US Pacific Air Forces spokesman Major Phil Ventura told reporters.  “The ADIZ has not changed our operations.”