A senior U.S. White House official visited South Korea Thursday to discuss the unilateral drawing of Beijing‘s air defense zone over the East China Sea.

Evan Medeiros, the senior director of Asian affairs at the National Security Council, was in Seoul and held talks with officials at the presidential office.

Mederios explained Washington’s stance on the air defense identification zone and expressed concerns that such a move will likely exert a negative influence on U.S.-China relations and with other countries in the region, according to a high-level official who requested anonymity. The official did not specify the exact time of the visit.

“Seoul also outlined its position on the ADIZ and its demand to Beijing to adjust it so as not to conflict with South Korea‘s identification zone,” the official said. He added that both sides concurred that China’s latest move has posed serious challenges, and the two countries agreed to work together on this issue.

China‘s zone, drawn over the weekend, overlaps with South Korea’s zone, near Jeju Island. Seoul already expressed regret over the overlap said it wants to resolve this manner as soon as possible.

Medeiros, meanwhile, exchanged views on Seoul‘s reservations about Japan’s moves to expand its right to collective self-defense.

“The NSC official said Washington understood Seoul‘s worries, but made clear Tokyo was within its rights to do so and that the United States supported such a move,” the source said.

After concluding his visit to Seoul, Medeiros flew to Japan to discuss similar issues, the source added.

The visit comes ahead of the planned visit by U.S. Vice President Joe Biden to South Korea, China and Japan next week. (Yonhap News)