A State Department spokeswoman said Sunday that the United States has accepted a plan by South Korea to expand its air defense identification zone in the East China Sea as the country notified potentially affected countries of it in advance.
The U.S. position was in marked contrast to its strong reaction to China's establishment of an ADIZ in the region last month without prior consultation.
"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," Jen Psaki said in a statement.
Psaki was referring to South Korea by its official name, the Republic of Korea.
South Korean President Park Geun Hye informed U.S. Vice President Joe Biden of the plan to expand the ADIZ during their meeting in Seoul on Friday, according to Psaki.
Psaki said the department appreciates South Korea's commitment to expand its ADIZ "in a manner consistent with international practice and respect for the freedom of overflight" in a bid to avoid "confusion for, or threats to, civilian airlines."
South Korea said Sunday it has decided to expand its ADIZ over the East China Sea starting Dec. 15, overlapping a similar air defense zone set up by China.
The U.S. government has criticized China for its unilateral establishment of an ADIZ that overlaps such zones operated by Japan, South Korea and Taiwan, and covers the Senkaku Islands, a group of Japan-administered islets that China claims.
In declaring its ADIZ in the East China Sea on Nov. 23, China said in a statement that aircraft flying in the identification zone must submit flight plans to Chinese authorities.
"China's armed forces will adopt defensive emergency measures to respond to aircraft that do not cooperate in the identification or refuse to follow the instructions," the statement said.
The United States has told China it does not accept the air defense zone and urged Beijing not to implement it.
The United States recognizes Japanese control of the Senkakus and says they are covered by a bilateral security treaty under which it is required to defend Japan.
ADIZ is a national defense perimeter to determine whether fighters should be scrambled when foreign aircraft enter without prior notification.