South Korea expands its air defense zone in reaction to China December 8, 2013 -- Updated 0931 GMT (1731 HKT) South Korea first sent planes into the area without notifying China It expands its air defense zone to include a disputed rock (CNN) -- In a move that is certain to anger China, South Korea has expanded its air defense zone to include an area claimed by both countries. Last month, China declared an Air Defense Identification Zone (ADIZ) in the East China Sea and declared that planes flying through it needed to file flight plans. The Chinese zone covers a disputed submerged rock in the Yellow Sea, known by Korea as Ieodo and by China as Suyan. Thumbing its nose at China's flight plan demand, South Korea first sent planes into the area without notifying China. And on Saturday, it expanded its air defense zone to include the rock. The new zone will go into effect on December 15. China didn't immediately respond to the South Korean move. But a spokeswoman for the State Department said Seoul had consulted with the United States ahead of time. "We appreciate the ROK's efforts to pursue this action in a responsible, deliberate fashion by prior consultations with the United States and its neighbors, including Japan and China," spokeswoman Jen Psaki said.